US President Donald Trump warned Iran that it will be held responsible if any more US forces are killed or injured in Iraq by Tehran-backed Iraqi militias.
Mr Trump's remarks on Twitter follow a rocket attack on the US embassy in Baghdad, the largest of its kind for 10 years, according to US Central Command (Centcom), the military headquarters responsible for US operations in the Middle East.
The embassy is regularly a target of Iraqi militias, as are joint Iraqi-US bases.
Mr Trump's warning is a departure for US policy.
In the past, the US blamed Iran for hundreds of lethal attacks by Iran-backed Iraqi militias, a fractious force known as the Popular Mobilisation Forces (PMF). But Washington has not gone as far as issuing a direct warning to Tehran – at least not publicly. Instead, the US preferred to pressure the Iraqi government to keep the groups under control.
Aware of the risk that the US will directly target them, Iran-backed PMF groups in recent months established new groups, claiming these new organisations are not linked to Iran. Attacks continue.
A massive barrage
A total of 21 rockets were reportedly fired, half of them landing in the sprawling embassy complex. Of the missiles that missed their target, at least one hit an Iraqi apartment block, while an Iraqi soldier near the embassy was injured.
A statement from Centcom said the attack was "almost certainly conducted by an Iranian-backed rogue militia group" and was "clearly not intended to avoid casualties".
Capt Bill Urban, who issued the statement, said it was "important for the people of Iraq to understand that past attacks by the Iranian-backed rogue militia groups have killed more Iraqi civilians and members of the Iraqi Security Forces than they have killed Americans".
Capt Urban also said the US would hold Iran responsible for any US casualties, although Centcom commander Gen Kenneth MacKenzie previously told The Wall Street Journal: "We do not seek a war, and I don't actually believe they seek one either," implying that the militias might exercise caution in future.
Kataib Hezbollah, one of the largest militant groups in the PMF, which has been accused of numerous similar attacks in the past, denied being behind the rocket barrage, calling it irresponsible. Qais Al Khazali, leader of the PMF group Asaib Ahl Al Haq, also denied the embassy attack in a tweet on Sunday, although he said that attacks on US forces in Iraq were "a right guaranteed by the laws of heaven".
On the brink of war
While most of the PMF rocket attacks have been off target, on December 27 last year one of the rockets killed an Iraqi-American contractor at a joint Iraqi-US base near the northern city of Kirkuk. US forces had been training and advising the Iraqi army, continuing the war against ISIS, at the invitation of the Iraqi government.
The US retaliated to the December 27 attack with air strikes – having long told the Iraqi government and the militias that US forces could legally defend themselves on Iraqi soil after an agreement with the government in Baghdad.
Dozens of Iran-backed militia fighters from Kataib Hezbollah were killed in subsequent US air strikes.
Pro-Iran groups then tried to storm the US embassy in Baghdad. At the time, the US received intelligence that Iranian Gen Qassem Suleimani, who oversaw advisory and funding efforts for the PMF, was meeting the de facto head of the PMF, Abu Mahdi Al Muhandis, in Baghdad.
Muhandis and Suleimani were killed on January 3 in a US drone strike near Baghdad airport.
Iran retaliated by firing ballistic missiles at two joint Iraqi-US bases on January 7, injuring 100 American soldiers and bringing Iran and the US to the brink of war.
The Iran-backed PMF groups have not backed down, continuing sporadic rocket attacks, often through front groups. As the anniversary of the death of Suleimani and Muhandis approaches, it is widely feared that Iran will launch a lethal attack against US forces in Iraq, once again raising the risk of war.