The United States has asked all American citizens to leave Iraq immediately.

The U.S. embassy in Iraq issued the warning on Friday morning, hours after a U.S. airstrike killed a top Iranian general, Al-Jazeera reports.

Qasem Soleimani, the leader of Iran’s elite Quds Force unit of the Iranian Revolutionary Guard Corps, was killed in an airstrike at the Baghdad International Airport, Iraq.

Mr Soleimani was killed alongside Abu Mahdi al-Muhandis, the leader of Kata’ib Hezbollah, also called Popular Mobilisation Forces (PMF) in Iraq.

The U.S. has confirmed that President Donald Trump ordered the airstrike.

“At the direction of the President, the U.S. military has taken decisive defensive action to protect U.S. personnel abroad by killing Qasem Soleimani, the head of the Iranian Revolutionary Guard Corps-Quds Force, a U.S.-designated Foreign Terrorist Organization,” the Pentagon said in a statement circulated on Twitter Friday morning.

Iran has condemned the attack and vowed to retaliate. The Iraqi government has also condemned the attack. Both the U.S. and Iran have a lot of influence in Iraq.

Influential Iraqi Shiite clerics and leaders, allied to Iran, have also condemned the attack, with many fearing there might be attacks on ordinary American citizens in Iraq.

In the U.S., there have been mixed reactions to the attack with Republican senators such as Marco Rubio and Lindsey Graham commending it while influential Democrats such as Joe Biden and Nancy Pelosi condemning it as not well thought out and putting U.S. interests in the Middle East at risk.

After the attack, Israel, a major U.S. ally, said it was increasing its defences in its borders with Lebanon and Syria.