Dozens of Iraqi protesters broke into the US embassy compound in Baghdad on Tuesday, smashing a main door and setting fire to a reception area, prompting tear gas and sounds of gunfire.
Witnesses reported rising from inside the compound and said they saw at least three US soldiers on the roof of the main building inside the embassy.
It was not clear what caused the fire at the reception area near the parking lot.
A man on a loudspeaker urged the protesters not to enter the compound, saying: "The message was delivered."
The US ambassador to Iraq and other staff were evacuated from the embassy.
Earlier, hundreds of protesters gathered outside the embassy to decry US air attacks in Iraq and Syria that killed 25 fighters from an Iran-backed Shia group.
Shouting "Down, Down USA!" the crowd hurled water bottles and smashed security cameras outside the embassy grounds.
Iraq's caretaker Prime Minister Adel Abdul Mahdi called on the protesters to leave the compound "immediately".
"We recall that any aggression or harassment of foreign embassies will be firmly prohibited by the security forces," Abdul Mahdi's office said several hours after the attack began.
The US military carried out the strikes on Sunday against the Iranian-backed Kataib Hezbollah. Washington claimed it was acting in retaliation for last week's killing of an American contractor in a rocket attack on an Iraqi military base that it blamed on the group.
The protesters raised flags of the powerful paramilitary group Hashd al-Shaabi (Popular Mobilisation Forces), of which Kataib Hezbollah is part, and several people climbed over the wall of the embassy and chanted "Death to America" and "No, no America", witnesses said.
Tuesday's attempted embassy storming took place after mourners held funerals for fighters killed in a Baghdad neighbourhood, after which they marched on to the heavily fortified Green Zone and kept walking until they reached the embassy.
Security guards were seen retreating to the inside of the compound. Protesters were also seen hanging yellow flags belonging to the Kataib Hezbollah on the walls.
Reporting from Baghdad, Al Jazeera's Simona Foltyn said there was no indication of an armed confrontation.
"This entire funeral procession, consisting mostly of PMF members and their followers, has entered through these gates without any resistance whatsoever from the Iraqi security forces that are supposed to guard the Green Zone," she said, speaking outside the US embassy.
"We've seen in the past when anti-government protesters were able to enter the Green Zone but I don't believe we've seen such a large number of people come this close to the US embassy," she continued, calling the development "significant".
"It remains to be seen how the authorities will react and more importantly, how the US will react," Foltyn added.
The US raids - the largest attack targeting an Iraqi state-sanctioned group in recent years - and the calls for retaliation represent a new escalation in the proxy war between the US and Iran playing out in the Middle East.
The US military said "precision defensive strikes" were conducted against five sites belonging to Kataib Hezbollah, which is a separate force from the Lebanese group Hezbollah, in Iraq and Syria.
Rejecting US influence
Marwan Bishara, Al Jazeera's senior political analyst, said that the embassy storming is indicative of Iraqis' rejection of US influence in their country.
"In terms of the United States, here is a country that has spent trillions of dollars in Iraq 16 years after its invasion and occupation to wins the hearts and minds of the Iraqi people, and ends up having its embassy surrounded the way it is," he said.
The "surreal" events on the ground have forced the US to go "on the defensive", Bishara added, where it "doesn't have much of an alliance either on the street or government institutions within Iraq".
He said, on the other hand, Iraqis have also been protesting against Iranian influence over the past few months.
"Countless people have demonstrated against Iranian presence and influence in the country, burning Iranian consulates," Bishara said.
"But there are others who are with the PMF and Kataib Hezbollah that remain loyal to Iran and are more than happy to deflect pressure on Iran by attacking the US embassy.
"So all in all, the tensions between Iran and the US continue, Iraq suffers in the process but Iran has a far easier win against the US because of its religious and ethnic influence within certain groups in the country," he said.
