In his victory speech, Mr Imamoglu said the result marked a "new beginning" for both the city and the country.
"We are opening up a new page in Istanbul," he said. "On this new page, there will be justice, equality, love."
He added that he was willing to work with Mr Erdogan, saying: "Mr President, I am ready to work in harmony with you."
Mr Imamoglu's lead of more than 775,000 votes marks a huge increase on his victory in March, when he won by just 13,000.
Who were the candidates?
Mr Imamoglu, 49, is from the secular Republican People's Party and is mayor of Istanbul's Beylikduzu district.
But his name was barely known before he ran for mayor in the March election.
Mr Yildirim was a founding member of Mr Erdogan's AKP and was prime minister from 2016 until 2018, when Turkey became a presidential democracy and the role ceased to exist.
He was elected Speaker of the new parliament in February and before that served as minister of transportation and communication.
Why was the previous result annulled?
Mr Imamoglu's narrow victory of 13,000 votes in March was not enough for Mr Yildirim to accept defeat.
The ruling party alleged that votes were stolen and many ballot box observers did not have official approval, leading the election board to demand a re-run of he vote.
Critics argue that pressure from President Erdogan was behind the decision.
Why is this election so important?
Mr Erdogan, who is from Istanbul, was elected mayor in 1994.
He founded the AKP in 2001 and served as prime minister between 2003 and 2014, before becoming president.
But cracks in the party are now beginning to show and analysts suggest these could be exacerbated by this loss.
"Erdogan is extremely worried," Murat Yetkin, a journalist and writer, said ahead of the vote.
"He is playing every card he has. If he loses, by whatever margin, it's the end of his steady political rise over the past quarter of a century," he added.
"In reality, he'll still be president, his coalition will still control parliament - although many will perceive his defeat as the beginning of the end for him."
The 'Peace to Prosperity' plan will be unveiled at a conference in Bahrain next week as the Trump administration looks to promote its economic vision for how to resolve the Israeli-Palestinian conflict.
Unveiling the proposal, President Donald Trump's son-in-law and senior adviser Jared Kushner said he welcomed "constructive criticism."
There was plenty of it.
Wary of what they see as a pro-Israel effort to undermine their cause without a serious attempt to find a political settlement that has eluded the region for generations, Palestinians and their backers in the Arab world rejected it out of hand.
"We don't need the Bahrain meeting to build our country," finance minister Shukri Bishara said Sunday.
“The sequence of (the plan) — economic revival followed by peace is unrealistic and an illusion," Bishara added.
The plan for economic revival would take effect only if a political solution is reached.
But there is no clear timeline and it remains unclear what Kushner and Jason Greenblatt, Trump's envoy overseeing the peace plan, have in mind on issues like an independent Palestinian state.
"I laugh when they attack this as the 'Deal of the Century'," Kushner said in an interview with Reuters on Saturday, referring to Palestinian leaders who have dismissed his plan as an attempt to buy off their aspirations for statehood.
"This is going to be the 'Opportunity of the Century' if they have the courage to pursue it," he added.
White House senior adviser Jared Kushner is interviewed at the Eisenhower Executive Office Building on June 20, 2019.Kevin Lamarque / Reuters
The Palestinians are furious at what they see as clear bias from the U.S. toward Israel.
In what was seen as another nod to the Israeli cause, U.S. ambassador to Israel David M. Friedman told The New York Times earlier this month that Israel had the right to annex at least some of the West Bank.
Many countries and international bodies consider Israeli settlements in eastern Jerusalem and the West Bank illegal because they are built on occupied land.
Meanwhile, the Palestinian economy has been in dire straits for years. Gaza’s economy has also been ravaged under the crippling Israel-Egyptian blockade since 2007.
"Generations of Palestinians have lived under adversity and loss, but the next chapter can be defined by freedom and dignity," the White House said.
Longtime Palestinian politician and leader Hanan Ashrawi was unimpressed.
“First lift the siege of Gaza, stop the Israeli theft of our land, resources and funds, give us our freedom of movement and control over our borders, airspace, territorial waters etc.,” he said in a tweet Saturday.
“Then watch us build a vibrant prosperous economy as a free and sovereign people.”
The Palestinian Authority is boycotting the Bahrain conference in protest to the U.S. approach, leading the White House not to invite the Israeli government.
In the wake of the economic plan's release Saturday, Palestinian President Mahmoud Abbas said focusing on economic issues "is unacceptable before the political situation is discussed.”
Abbas said that Trump's broader peace plan will not succeed "because it ends the Palestinian cause."
The Palestinian president said that the American scheme adopts Israel's visions and neglects the longstanding two-state solution to the conflict.
"Palestine is not for sale," Ismail Rudwan, an official with Islamic militant group Hamas that governs Gaza, told NBC News.
"We affirm our rejection to the deal of the century with all its political, economic and security dimensions."
In a comment to NBC News before the economic plan was unveiled, Fawaz Gerges, a professor of Middle Eastern politics at the London School of Economics and Political Science, said the Bahrain conference had “exposed” that the Trump administration’s peace plan was about providing the Palestinians with economic help in exchange for them giving up their aspirations to establish a Palestinian state.
In the process, he said Trump was dismantling decades of an international consensus.
The plan was rejected not only by Palestinian leaders, but also figures in Arab states whose help Washington is actively seeking.
It promised billions of dollars to Jordan, Lebanon and Egypt, which have absorbed Palestinian refugees and dealt with other ramifications of the conflict for decades.
But on Sunday the Lebanese parliament's speaker said the country does not want investment at the expense of the Palestinian cause.
"Mr. Kushner, Lebanon and the Lebanese will not be false witnesses for selling Palestine," Nabih Berri said.
At home the U.S. plan, released quietly on the Sabbath, was met with a muted response but some criticism.
“Even an ambitious vision of much-needed economic development cannot substitute for a political agreement that will finally resolve the core issues driving the Israeli-Palestinian conflict,” said Jeremy Ben-Ami, president of J Street, a Washington-based liberal advocacy group.
Israel controls the economic life of the Palestinian Territoties. None of Kushner’s proposals are remotely possible without Israeli acquiesce. Yet his 40 page plan calls on Israel to do precisely nothing https://t.co/kgLjcxbCz6
It also drew mixed responses from the political establishment in Israel.
Tzachi Hanegbi, a cabinet member close to Prime Minister Benjamin Netanyahu, called Palestinians' rejection of the plan tragic.
But Ayman Odeh, leader of the party that represents Israel's Arabs, said Sunday that the only solution to the conflict is to establish an independent Palestinian state alongside the State of Israel.
“Someone needs to explain to Trump that you can’t buy everything with money," Israel’s daily Ma’ariv newspaper quoted him as saying.
"Certainly not the Palestinian people’s just national aspirations.”
Bolton also warned of the possibility of a strike against Iran in the future during a meeting with Israeli Prime Minister Benjamin Netanyahu in Jerusalem.
"Neither Iran nor any other hostile actor should mistake US prudence and discretion for weakness. No one has granted them a hunting license in the Middle East," Bolton, who has publicly and repeatedly called for regime change in Tehran in the past, said.
After coming within minutes of military strikes, Trump stepped back from the brink of a dangerous escalation Thursday.
The President said Friday he called off an attack because he decided there would be too many deaths for a proportionate response to the downing of the US drone.
The President's stance on the dramatic escalation in tensions with Iran has been in stark contrast to harsh public warnings from Secretary of State Mike Pompeo and particularly the views of Bolton.
Referring to Trump's decision to call of the strike, Bolton threatened possible military action in the future. "The President said, 'I just stopped the strike from going forward... at this time,'" said Bolton on Sunday.
"As President Trump said on Friday, our military is rebuilt, new, and ready to go -- by far the best in the world," Bolton said. "Sanctions are biting, and more were added last night. Iran can never have nuclear weapons, not against the USA, not against the world."
Bolton concluded his remarks by saying, "Stay tuned."
Meanwhile the United Arab Emirates' foreign minister said Sunday that a de-escalation of tensions in the Gulf region could only be achieved via a "political solution."
"Tensions in the Gulf can only be addressed politically," the Minister of State for Foreign Affairs for the United Arab Emirates, Anwar Gargash, wrote on Twitter, adding that the crisis requires "collective attention" to find a solution through "dialogue and negotiations."
"Regional voices (are) important to achieve sustainable solutions" to a crisis which has been "long in the making," he added.
In response to Bolton's comments, Iran's foreign minister said the "B team" -- a term he has used to collectively reference Netanyahu, Bolton, UAE Crown Prince Mohammed bin Zayed, and Saudi Crown Prince Mohammed bin Salman -- was "moments away from trapping [President Trump] into war" with Iran.
"Prudence prevented it," Iran's Foreign Minister, Mohammad Javad Zarif, said on Twitter Sunday, in an apparent nod to Trump calling off the attacks Thursday. But added that the Trump' administration's policy of maximum pressure "brings tension."
He added that he had "more evidence" of a planned attack involving "encroachment of a MQ9 spy drone," the purchase of speedboats and "phone calls planning to attribute ship attacks to Iran."
'Make Iran great again'
Tensions have spiked in the region since the US withdrew from the Obama-era nuclear deal with Iran last year.
The US standoff with Iran escalated Monday when the Trump administration announced the deployment of 1,000 additional troops and extra military resources to the Middle East.
By Thursday, the Revolutionary Guard Corps said it had shot down an "intruding American spy drone" after it entered Iranian territory.
The location of the drone's downing has been a point of contention, with the Trump administration insisting the drone was in international airspace over the Strait of Hormuz.
The incident has left Trump caught between some Republicans demanding a response and congressional Democrats warning that the President -- and the Iran policy hard-liners on his national security staff -- could lose control of the situation and lead the United States into war.
He said Saturday that the US is putting additional sanctions on Iran and he would support a course of action to "make Iran great again" should Tehran agree to a nuclear weapons ban.
Vice President Mike Pence told CNN's Jake Tapper on "State of the Union" Sunday that Trump will announce new sanctions on Iran on Monday. Pence declined to say what those sanctions would look like.
CNN's Kevin Liptak, Nicole Gaouette and Nada Bashir contributed to this report.
Bolton also warned of the possibility of a strike against Iran in the future during a meeting with Israeli Prime Minister Benjamin Netanyahu in Jerusalem.
"Neither Iran nor any other hostile actor should mistake US prudence and discretion for weakness. No one has granted them a hunting license in the Middle East," Bolton, who has publicly and repeatedly called for regime change in Tehran in the past, said.
After coming within minutes of military strikes, Trump stepped back from the brink of a dangerous escalation Thursday.
The President said Friday he called off an attack because he decided there would be too many deaths for a proportionate response to the downing of the US drone.
The President's stance on the dramatic escalation in tensions with Iran has been in stark contrast to harsh public warnings from Secretary of State Mike Pompeo and particularly the views of Bolton.
Referring to Trump's decision to call of the strike, Bolton threatened possible military action in the future. "The President said, 'I just stopped the strike from going forward... at this time,'" said Bolton on Sunday.
"As President Trump said on Friday, our military is rebuilt, new, and ready to go -- by far the best in the world," Bolton said. "Sanctions are biting, and more were added last night. Iran can never have nuclear weapons, not against the USA, not against the world."
Bolton concluded his remarks by saying, "Stay tuned."
Meanwhile the United Arab Emirates' foreign minister said Sunday that a de-escalation of tensions in the Gulf region could only be achieved via a "political solution."
"Tensions in the Gulf can only be addressed politically," the Minister of State for Foreign Affairs for the United Arab Emirates, Anwar Gargash, wrote on Twitter, adding that the crisis requires "collective attention" to find a solution through "dialogue and negotiations."
"Regional voices (are) important to achieve sustainable solutions" to a crisis which has been "long in the making," he added.
'Make Iran great again'
Tensions have spiked in the region since the US withdrew from the Obama-era nuclear deal with Iran last year.
The US standoff with Iran escalated Monday when the Trump administration announced the deployment of 1,000 additional troops and extra military resources to the Middle East.
By Thursday, the Revolutionary Guard Corps said it had shot down an "intruding American spy drone" after it entered Iranian territory.
The location of the drone's downing has been a point of contention, with the Trump administration insisting the drone was in international airspace over the Strait of Hormuz.
The incident has left Trump caught between some Republicans demanding a response and congressional Democrats warning that the President -- and the Iran policy hard-liners on his national security staff -- could lose control of the situation and lead the United States into war.
He said Saturday that the US is putting additional sanctions on Iran and he would support a course of action to "make Iran great again" should Tehran agree to a nuclear weapons ban.
CNN's Kevin Liptak, Nicole Gaouette and Nada Bashir contributed to this report.
ADDIS ABABA, Ethiopia — A coup attempt by a renegade general in one of Ethiopia’s largest regional states resulted in the death of four officials, including the national army’s chief of staff and the president of the region, the government announced Sunday.
On Saturday evening, gunmen attacked an executive meeting of the Amhara regional state in the city of Bahir Dar killing its president Ambachew Mekonnen and his top adviser and grievously injuring the regional attorney general. Hours later, in the capital Addis, the bodyguard of army chief of staff Gen. Seare Mekonnen opened fire on him, killing him and an associate.
Government spokeswoman Bilene Seyoum blamed the attack on a recently amnestied brigadier general who had been imprisoned for his political views by the previous government several years before.
“The coup attempt and attack was orchestrated by Brig. Gen. Asaminew Tsige, the Amhara peace and security head with other agents,” she told journalists. “He and his colleagues were given amnesty over the last year by the new administration amid efforts to integrate them back to regular life.”
She said most of the perpetrators, including Seare’s bodyguard, were in custody and operations were underway to sweep up the remaining accomplices. The Amhara region was “currently under 100 percent control.”
Ethiopia, Africa’s second largest country by population, is a key U.S. ally in the fight against terror in the Horn of Africa and an important source of stability in the restive region.
The country’s politics have undergone a dramatic change over the last year, with the arrival of new reformist prime minister who has invited back exiled opposition politicians and guerrilla groups as well as freed thousands of political prisoners.
Asaminew had been imprisoned by the previous regime for his opposition to the government and his release and appointment to head of security was part of the larger reconciliation process.
The new freedoms, however, have allowed long simmering tensions to rise to the surface and millions have been displace in ethnic-based land conflicts around the country.
In 2018, with some 3 million driven from their homes, Ethiopia had the largest number of newly displaced in the world.
There has also been a great deal of political ferment in the ethnic-based regions that make up the country with the rise of nationalist ethnic groups pushing for greater regional autonomy from the central government.
As news of the coup attempt in Bahir Dar and the attack on the chief of staff’s home in the heart of the capital trickled out Saturday night, social media exploded with rumors and speculation over what was taking place. Within a few hours, all access to the Internet had been shut down and army and police checkpoints sprung up around the capital.
Abiy, the prime minister, appeared on television at midnight dressed in military fatigues to call for calm and ensure the country that the situation was under control.
Since coming to power, Abiy made piece with long time rival Eritrea and has been active in brokering peace deals between fractious neighbors in the region.
Most recently he has been active in mediating between the military transitional rulers in Sudan and protesters.
U.S. national security adviser John Bolton had a message for Iran on Sunday during his visit to Israel: He advised the leaders of the Islamic nation not to “mistake U.S. prudence and discretion for weakness.”
Bolton’s comment followed Friday’s confirmation by President Trump that he had called off a planned retaliatory attack against Iran following that country’s downing of a U.S. military drone Thursday in international airspace over the Strait of Hormuz.
Trump said he reconsidered action after deciding that the potential loss of life in a military action was not “proportionate” after Iran had attacked an unmanned aircraft.
U.S. National Security Advisor John Bolton gives statements to media in Jerusalem, Sunday, June 23, 2019. (Associated Press)
On Saturday, Trump praised Bolton, saying he had confidence in his appointee despite some disagreements on some Mideast issues, Politico reported.
Bolton added Sunday that no one had granted Iran “a hunting license in the Middle East,” as he spoke alongside Israeli Prime Minister Benjamin Netanyahu during his Mideast visit.
Late last month, Bolton had charged that Iran was responsible for attacks against oil tankers off the coast of the United Arab Emirates – and warned that the U.S. would strike back if attacked.
Bolton said Iran was “almost certainly” responsible for the tanker attacks.
Rhetoric between the U.S. and Iran has been sharpening in recent weeks as Iran feels the effects of sanctions imposed by the U.S. following Trump’s decision to withdraw from a 2015 nuclear agreement that Iran had negotiated with the U.S. and other world powers during the Obama administration.
Trump had repeatedly criticized the deal as not going far enough to ensure that Iran was not pursuing nuclear weapons.
Fox News’ Bradford Betz and Lukas Mikelionis and the Associated Press contributed to this report.
