Iran Supreme Leader Ayatollah Ali Khamenei on Friday vowed to take “severe revenge” against those responsible for the death of Iran’s elite Quds Force chief, Major General Qassem Soleimani, AFP reported. Iran President Hassan Rouhani promised that “free nations of the region” would avenge Soleimani.

Soleimani and top Iraqi militia commander Abu Mahdi al-Muhandis were killed in an United States airstrike at the Baghdad international airport early on Friday. Al-Muhandis was the deputy commander of Iran-backed Iraqi militias known as the Popular Mobilisation Forces, or PMF. He was reportedly an advisor to Soleimani. The Pentagon confirmed that US President Donald Trump had ordered the strikes.

“Martyrdom was the reward for his ceaseless efforts in all these years,” Khamenei said in a tweet, referring to Soleimani. “With him gone, God willing, his work and his path will not be stopped, but severe revenge awaits the criminals who bloodied their foul hands with his blood and other martyrs’ in last night’s incident.”

Khamenei also declared three days of mourning for Soleimani. The death of Iran’s most revered military leader is expected to be potential turning point in West Asia, and may draw severe retaliation from Iran and the forces it backs in the region against Israel and American interests.

Iran Foreign Minister Mohammad Javad Zarif criticised the American action as foolish. “The US’ act of international terrorism, targeting and assassinating General extremely dangerous and a foolish escalation,” Zarif wrote on Twitter. “The US bears responsibility for all consequences of its rogue adventurism.”

“The malice and stupidity of America’s terrorist forces in assassinating General Soleimani, this hero martyr and the leader of combatting terrorism and extremism, will certainly further empower the tree of resistance in the region and the world,” the Foreign Ministry said in a statement.

The ministry added that it would “use all its political legal and international capacities to enact the decisions of the Supreme National Security Council to make the murderous and terrorist regime of America answer for this clear atrocity.”

After the deaths were confirmed, United States President Donald Trump tweeted an image of the US flag without any explanation.

“General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region,” the US Department of Defense said in a statement. “General Soleimani and his Quds Force were responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more.”

“This strike was aimed at deterring future Iranian attack plans,” it said, adding that the United States would continue to take necessary action to protect Americans and interests around the world.

The attack came after Trump had blamed Iran for “orchestrating” the attack on the US embassy in Baghdad and said he would hold Tehran responsible.

Americans urged to leave Iraq

Meanwhile, the United States embassy in Baghdad on Friday urged its citizens to “depart Iraq immediately”, fearing the consequences of Soleimani’s assassination.

“US citizens should depart via airline while possible, and failing that, to other countries via land,” the embassy added. “Due to Iranian-backed militia attacks at the US Embassy compound, all public consular operations are suspended until further notice. US citizens should not approach the Embassy.”