Dozens of angry Iraqi Shiite militia supporters broke into the U.S. Embassy compound in Baghdad on Tuesday after smashing a main door and setting fire to a reception area, prompting tear gas and sounds of gunfire.

An Associated Press reporter at the scene saw flames rising from inside the compound and at least three U.S. soldiers on the roof of the main building inside embassy. There was a fire at the reception area near the parking lot of the compound but it was unclear what had caused it. A man on a loudspeaker urged the mob not to enter the compound, saying: "The message was delivered."

The embassy attack followed deadly U.S. airstrikes on Sunday that killed 25 fighters of the Iran-backed militia in Iraq, the Kataeb Hezbollah. The U.S. military said it was in retaliation for last week's killing of an American contractor in a rocket attack on an Iraqi military base that it had blamed on the militia.

Dozens of protesters pushed into the compound after smashing the gate used by cars to enter the embassy. The protesters, many in militia uniform, stopped in a corridor after about 5 meters (16 feet), and were only about 200 meters away from the main building. Half a dozen U.S. soldiers were seen on the roof of the main building, their guns were pointed at the protesters.

Smoke from the tear gas rose in the area, and at least three of the protesters appeared to have difficulties breathing. It wasn't immediately known whether the embassy staff had remained inside the main building.

The protesters hanged a poster on the wall: "America is an aggressor."

Earlier, the mob shouted "Down, Down USA!" as the crowd tried to push inside the embassy grounds, hurling water and stones over its walls. They raised yellow militia flags and taunted the embassy's security staff who remained behind the glass windows in the gates' reception area and also sprayed graffiti on the wall and windows. The graffiti, in red in support of the Kataeb Hezbollah, read: "Closed in the name of the resistance."

Also, hundreds of angry protesters set up tents outside the embassy. As tempers rose, the mob set fire to three trailers used by security guards along the embassy wall.

No one was immediately reported hurt in the rampage and security staff had withdrawn to inside the embassy earlier, soon after protesters gathered outside.

Seven armored vehicles with about 30 Iraqi soldiers arrived near the embassy hours after the violence erupted, deploying near the embassy walls but not close to the breached area.

There was no immediate comment from the Pentagon and the State Department on the breach of the U.S. Embassy in Baghdad.

The U.S. airstrikes — the largest targeting an Iraqi state-sanctioned militia in recent years — and the subsequent calls by the militia for retaliation, represent a new escalation in the proxy war between the U.S. and Iran playing out in the Middle East.

Tuesday's attempted embassy storming took place after mourners and supporters held funerals for the militia fighters killed in a Baghdad neighborhood, after which they marched on to the heavily fortified Green Zone and kept walking till they reached the sprawling U.S. Embassy there.

AP journalists then saw the crowd as they tried to scale the walls of the embassy, in what appeared to be an attempt to storm it, shouting "Down, down USA!" and "Death to America" and "Death to Israel."

U.S. Secretary of State Mike Pompeo said Sunday's strikes send the message that the U.S. will not tolerate actions by Iran that jeopardize American lives.

The Iranian-backed Iraqi militia had vowed Monday to retaliate for the U.S. military strikes. The attack and vows for revenge raised concerns of new attacks that could threaten American interests in the region.

The U.S. attack also outraged both the militias and the Iraqi government, which said it will reconsider its relationship with the U.S.-led coalition — the first time it has said it will do so since an agreement was struck to keep some U.S. troops in the country. It called the attack a "flagrant violation" of its sovereignty.

In a partly televised meeting Monday, Iraqi Prime Minister Adel Abdul-Mahdi told Cabinet members that he had tried to stop the U.S. operation "but there was insistence" from American officials.

The U.S. military said "precision defensive strikes" were conducted against five sites of Kataeb Hezbollah, or Hezbollah Brigades in Iraq and Syria. The group, which is a separate force from the Lebanese militant group Hezbollah, operates under the umbrella of the state-sanctioned militias known collectively as the Popular Mobilization Forces. Many of them are supported by Iran.