Iran promised to seek revenge for a U.S. airstrike near Baghdad’s airport that killed the mastermind of its interventions across the Middle East, and the U.S. said Friday it was sending thousands more troops to the region as tensions soared in the wake of the targeted killing.

The death of Gen. Qassem Soleimani, the head of Iran’s elite Quds Force, marks a major escalation in the standoff between Washington and Iran, which has careened from one crisis to another since President Donald Trump withdrew from the 2015 nuclear deal and imposed crippling sanctions.

2:32 U.S. kills top Iranian general in air strike at Baghdad airport U.S. kills top Iranian general in air strike at Baghdad airport

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In more violence, another airstrike almost exactly 24 hours after the one that targeted Soleimani killed five members of an Iran-backed militia north of Baghdad, an Iraqi security official said, speaking on condition of anonymity because he was not authorized to talk to reporters.

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The Iran-backed Popular Mobilization Forces confirmed the strike, saying it hit one of its medical convoys near the stadium in Taji, north of Baghdad. The group said none of its top leaders were killed. A U.S. official said the attack was not an American military attack. The official spoke on condition of anonymity.

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The targeted strike against Soleimani and any retaliation by Iran could ignite a conflict that engulfs the whole region, endangering U.S. troops in Iraq, Syria and beyond. Over the last two decades, Soleimani had assembled a network of heavily armed allies stretching all the way to southern Lebanon, on Israel’s doorstep.

“We take comfort in knowing that his reign of terror is over,” Trump said of Soleimani.

Still, the United States said it was sending nearly 3,000 more Army troops to the Middle East, reflecting concern about potential Iranian retaliation for the killing. The U.S. also urged American citizens to leave Iraq “immediately” following the early morning airstrike at Baghdad’s international airport that Iran’s state TV said killed Soleimani and nine others. The State Department said the embassy in Baghdad, which was attacked by Iran-backed militiamen and their supporters earlier this week, is closed and all consular services have been suspended.

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Around 5,200 American troops are based in Iraq to train Iraqi forces and help in the fight against Islamic State group militants. Defence officials who discussed the new troop movements spoke on condition of anonymity to discuss a decision not yet announced by the Pentagon. A Pentagon official who was not authorized to be identified said the U.S. also had placed an Army brigade on alert to fly into Lebanon to protect the American Embassy. U.S. embassies also issued a security alert for Americans in Bahrain, Kuwait and Nigeria.

The U.S. announcement about sending more troops came as Trump said Soleimani’s killing was not an effort to begin a conflict with Iran. “We took action last night to stop a war. We did not take action to start a war,” Trump said, adding that he does not seek regime change in Iran.

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Iran’s Supreme Leader Ayatollah Ali Khamenei vowed “harsh retaliation” after the airstrike, calling Soleimani the “international face of resistance.” Khamenei declared three days of public mourning and appointed Maj. Gen. Esmail Ghaani, Soleimani’s deputy, to replace him as head of the Quds Force.

Iranian President Hassan Rouhani called the killing a “heinous crime” and said his country would “take revenge.” Iran twice summoned the Swiss envoy, the first time delivering a letter to pass onto Washington.

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Iranian Foreign minister Mohammad Javad Zarif called the U.S. attack a “cowardly terrorist action” and said Iran has the right to respond “in any method and any time.“

Thousands of worshipers in Tehran took to the streets after Friday prayers to condemn the killing, waving posters of Soleimani and chanting “Death to deceitful America.”

However, the attack could act as a deterrent for Iran and its allies to delay or restrain any potential response. Trump said possible targets had been identified and the U.S. was prepared. Oil prices surged on news of the airstrike and markets were mixed.

1:39 Qassem Soleimani: Who he was and why the United States killed him Qassem Soleimani: Who he was and why the United States killed him

The killing promised to further strain relations with Iraq’s government, which is allied with both Washington and Tehran and has been deeply worried about becoming a battleground in their rivalry. Iraqi politicians close to Iran called for the country to order U.S. forces out.

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The Defence Department said it killed the 62-year-old Soleimani because he “was actively developing plans to attack American diplomats and service members in Iraq and throughout the region.” It also accused Soleimani of approving orchestrated violent protests at the U.S. Embassy in Baghdad.

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The strike, on an access road near Baghdad’s airport, was carried out early Friday by an American drone, according to a U.S. official.

Soleimani had just disembarked from a plane arriving from either Syria or Lebanon, a senior Iraqi security official said. The blast tore his body to pieces along with that of Abu Mahdi al-Muhandis, deputy commander of the Iranian-backed militias in Iraq known as the Popular Mobilization Forces. A senior politician said Soleimani’s body was identified by the ring he wore. Iran’s state TV said Friday 10 people were killed, including five Revolutionary Guard members and Soleimani’s son-in-law.

The officials spoke on condition of anonymity because they were not authorized to talk to reporters.

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The attack comes at the start of a year in which Trump faces both a Senate trial following his impeachment by Congress and a re-election campaign. It marks a potential turning point in the Middle East and represents a drastic change for American policy toward Iran after months of tensions.

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The tensions are rooted in Trump’s decision in May 2018 to withdraw the U.S. from Iran’s nuclear deal with world powers, struck under his predecessor, Barack Obama.

….of PROTESTERS killed in Iran itself. While Iran will never be able to properly admit it, Soleimani was both hated and feared within the country. They are not nearly as saddened as the leaders will let the outside world believe. He should have been taken out many years ago! — Donald J. Trump (@realDonaldTrump) January 3, 2020

Since then, Tehran shot down a U.S. military surveillance drone and seized oil tankers. The U.S. also blames Iran for other attacks targeting tankers and a September assault on Saudi Arabia’s oil industry that temporarily halved its production.

Supporters of the strike against Soleimani said it restored U.S. deterrence power against Iran, and Trump allies were quick to praise the action. “To the Iranian government: if you want more, you will get more,” South Carolina Sen. Lindsey Graham tweeted.

“Hope this is the first step to regime change in Tehran,” Trump’s former National Security Adviser, John Bolton, wrote in a tweet.

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Others, including Democratic White House hopefuls, criticized Trump’s order. Democratic presidential candidate Joe Biden said Trump had “tossed a stick of dynamite into a tinderbox,” saying it could leave the U.S. “on the brink of a major conflict across the Middle East.”

Trump, who was vacationing at his private club in Palm Beach, Florida, said he ordered the airstrike because Soleimani had killed and wounded many Americans over the years and was plotting to kill many more. “He should have been taken out many years ago,” he added.

The potential for a spiraling escalation alarmed U.S. allies and rivals alike.

“We are waking up in a more dangerous world,” France’s deputy minister for foreign affairs, Amelie de Montchalin, told RTL radio. The European Union warned against a “generalized flare-up of violence.” Russia condemned the killing, and fellow Security Council member China said it was “highly concerned.” Britain and Germany noted that Iran also bore some responsibility for escalating tensions.

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While Iran’s conventional military has suffered under 40 years of American sanctions, Iran can strike in the region through its allied forces like Lebanon’s Hezbollah, Iraqi militias and Yemen’s Houthi rebels. Hezbollah leader Hassan Nasrallah called on “the resistance the world over” to avenge Soleimani’s killing. Frictions over oil shipments in the Gulf could also increase, and Iran’s elite Revolutionary Guard has built up a ballistic missile program.

Iran’s Supreme National Security Council said it in a statement Friday that it had held a special session and made “appropriate decisions” on how to respond, but didn’t elaborate.

Israeli Defence Minister Naftali Bennett held a meeting with top security officials Friday, but the Israeli military said it was not taking any extraordinary action on its northern front, other than closing a ski resort in the Golan Heights near Lebanon and Syria as a precaution.

The most immediate impact could be in Iraq. Funerals for al-Muhandis and the other slain Iraqis were set for Saturday.

Prime Minister Adel Abdul-Mahdi condemned the strike as an “aggression against Iraq.” An emergency session of parliament was called for Sunday, which the deputy speaker, Hassan al-Kaabi, said would take “decisions that put an end to the U.S. presence in Iraq.”

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