The State Department issued a security alert early Friday morning urging Americans in Iraq to leave the country immediately.

The warning comes hours after Iran promised “harsh retaliation” against the United States for an airstrike that killed top Iranian Gen. Qassem Soleimani at the Baghdad International Airport.

“Due to heightened tensions in Iraq and the region, we urge U.S. citizens to depart Iraq immediately,” the State Department said in the alert.

“US citizens should depart via airline while possible, and failing that, to other countries via land. Due to Iranian-backed militia attacks at the U.S. E

Iran’s leadership has vowed to take revenge, and the country has multiple unconventional ways to do so, ranging from cyber attacks on US networks to assaults on US forces in the Gulf region.

The US strike on Soleimani came days after protesters angered by US airstrikes hurled stones and demonstrated outside the US Embassy in Baghdad on Tuesday, to which US forces responded by firing tear gas.

Many US allies are also warning that the Soleimani strike will risk the world going to war.

“We are waking up in a more dangerous world,” France’s deputy minister of foreign affairs told the local RTL radio on Friday morning, according to the Associated Press.