The United States Embassy in the Iraqi capital Baghdad has been hit by a missile attack that caused smoke to rise from the building.

An Iraqi security source told Al Jazeera on Saturday that the attack destroyed part of its air defence system, without giving further details.

A missile struck a helipad inside the US Embassy in Baghdad, two security officials told The Associated Press news agency.

The projectile landed within the embassy’s boundaries in the Green Zone, the heavily fortified district in central Baghdad that houses Iraqi government institutions and foreign embassies, added the security officials, who spoke on condition of anonymity as they are not authorised to speak with the press.

Hours later, the US Embassy in Baghdad urged US citizens in Iraq to leave immediately as it updated its security alert.

“US citizens choosing ⁠to remain in ⁠Iraq are strongly encouraged to reconsider ⁠in light ⁠of the ⁠significant threat posed by Iran-aligned terrorist ‌militia groups,” the embassy said.

Videos posted by social media users showed smoke rising from the compound after the attack.

Al Jazeera’s Mahmoud Abdelwahed, reporting from Baghdad, said there was no immediate statement on whether there were casualties or the exact extent of damage in the attack.

“But we understand that Iran-aligned armed groups in Iraq have always pledged to attack US facilities, especially the embassy,” he said, adding that they want to avenge the death of Ayatollah Ali Khamenei, the former supreme leader, who was assassinated, along with family members, by a US-Israeli air strike at the beginning of this war.

“In fact, yesterday, they issued a statement putting $100,000 as a reward to anyone who provides information leading to any US diplomatic personnel inside the country,” our correspondent said, adding that some of the personnel were “taking shelter in civilian houses”.

Second attack

It is the second time the US Embassy has come under attack in Baghdad since the start of the war.

On Friday, the embassy renewed its Level 4 security alert for Iraq, warning that Iran and Iran-aligned armed groups have previously carried out attacks against US citizens, interests and infrastructure, and “may continue to target them”.

The sprawling embassy complex, one of the largest US diplomatic facilities in the world, has been repeatedly attacked by rockets and drones in the past.

Several Tehran-backed armed groups, which Washington has designated as “terrorist organisations”, allied under an umbrella movement known as the Islamic Resistance in Iraq, have claimed daily drone and rocket attacks against US bases in the region.

Since the start of the war, several attacks against members of those groups across Iraq have been blamed on the US and Israel.

Saturday’s attack took place shortly after two strikes hit the powerful Iran-backed Kataib Hezbollah, which is part of the Popular ⁠Mobilisation Forces, killing three of its members, security sources told the Reuters and AFP news agencies.

Iraq has seen attacks from both sides of the conflict: Iran and its proxies target US bases while the US has bombed pro-Iran groups.

Iraq, long a proxy battleground between the US and Iran, was quickly dragged into this sprawling Middle East war triggered by US and Israeli strikes on Iran on February 28.