Iranian Supreme Leader Ayatollah Ali Khamenei vowed “harsh vengeance” against the United States following an airstrike that killed Commander of the Islamic Revolution Guards Corps (IRGC) Quds Force Major General Qasem Soleimani on Thursday.

A U.S. airstrike targeted a convoy carrying Soleimani and at least three other militiamen at Baghdad’s International Airport. The killing is widely considered to be a major blow to the Iranian regime just days after members of Iranian proxy militias attempted to storm the U.S. embassy in Baghdad.

In a statement Thursday evening, the Department of Defense confirmed that they had “taken decisive defensive action to protect U.S. personnel abroad by killing Qasem Soleimani, the head of the Iranian Revolutionary Guard Corps Qods Force, a U.S.-designated Foreign Terrorist Organization.”

According to state-run Tasmin News Agency, Khamenei “expressed his condolences” over the assassination, warning that a “harsh vengeance awaits the criminals who have the blood of him (General Soleimani) and the other martyrs of last night’s incident on their hands.”

He went on to describe Soleimani as “an international resistance figure” before declaring three days of mourning nationwide.

Iranian President Hassan Rouhani said in his statement on Friday that Iran and “other freedom-loving nations will take revenge for Soleimani’s blood.”

There were also negative reactions from the Iraqi government, with caretaker Prime Minister Adel Abdel-Mahdi condemning the U.S. attack as “aggression on Iraq as a state, its government, and people.”

“Carrying out physical liquidation operations against leading Iraqi figures or from a brotherly country on the Iraqi lands is a flagrant violation of Iraq’s sovereignty and a dangerous escalation that triggers a destructive war in Iraq, the region and the world,” Abdel-Mahdi said.

Abdel-Mahdi technically resigned from office in November following months of protests against his government for allowing Iran to colonize large parts of Iraq through policies like legalizing Iranian militias as formal wings of the Iraqi military. He remains in office because Baghdad has failed to organize a succession process or election.

Soleimani commanded the IRGC’s Quds Force, its specialized terrorism unit, since 1998. He was instrumental in many of Iran’s military operations, including its role in the civil wars in Syria and Yemen and operations against the governments of Jordan and Lebanon.

The Pentagon said following his death that Soleimani was “actively developing plans to attack American diplomats and service members in Iraq and throughout the region”:

General Soleimani and his Qods (Quda) Force were responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more. He had orchestrated attacks on coalition bases in Iraq over the last several months – including the attack on December 27th – culminating in the death and wounding of additional American and Iraqi personnel. General Soleimani also approved the attacks on the U.S. Embassy in Baghdad that took place this week.

President Donald Trump appeared to celebrate on Twitter by posting the American flag.

As part of their immediate response, Tehran has demanded that the Swiss charges d’affaires, who represents U.S. interests in Tehran, condemn the killing, with Iranian Foreign Minister Mohammad Javad Zarif declaring the strike “an act of state terrorism and violation of Iraq’s sovereignty.”

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