Thousands of demonstrators participating in the mourning of the Hashd Shaabi (Popular Mobilization Forces) members killed by U.S. airstrikes in Iraq gathered Tuesday outside the U.S. embassy in Baghdad.

The protesters are supporters of pro-Iran factions.

The U.S. ambassador and other staff have been evacuated from the embassy, according to Iraqi Foreign Ministry officials.

Iraqi Prime Minister Adel Abdul Mahdi urged crowds who had entered the U.S. embassy compound to leave "immediately."

"We recall that any aggression or harassment of foreign embassies will be firmly prohibited by the security forces," Mahdi's office said several hours after the rally began.

The demonstrators entered the heavily fortified Green Zone and prepared tents to hold a sit-in protest in front of the embassy, an official from the Iraqi Interior Ministry told Xinhua on condition of anonymity.

U.S. security forces inside the compound fired tear gas and flash bangs to disperse the crowds, which had ignored calls over megaphones to back away from the embassy.

The U.S. airstrikes were in response to a 36-rocket attack last week that killed one American contractor at an Iraqi base, the latest in a string of attacks on areas where U.S. troops are deployed.

No group claimed responsibility for the attack, but U.S. security assessments have largely blamed them on Kataeb Hezbollah.

U.S. President Donald Trump said Tuesday that he expects Iraq to "use its forces" to protect the U.S. embassy in Baghdad.

"Now Iran is orchestrating an attack on the US Embassy in Iraq. They will be held fully responsible," he tweeted.

(With input from AFP)