Two American personnel and one from the UK were killed and about a dozen people were wounded when 15 small rockets hit Iraq’s Taji military camp north of Baghdad on March 11, two US officials told Reuters, citing preliminary information that could change. The French Press Agency reported that the dead were a US soldier, a US contractor and a British soldier.

The officials who spoke to Reuters added that it was too early to assign blame—but if the conclusion was drawn that Iran-backed militia were responsible, the attack could spark a new phase of military escalation between the US and Iran. Within hours after the attack, there were reports of air strikes conducted by unidentified aircraft on an area of the Iraqi-Syrian border used as a base by an Iran-backed militia.

The officials reportedly declined to quantify the number of troops and military contractors among the dead and wounded. The information was just coming in and could change, they were quoted as saying. Initial battlefield reports often contain inaccuracies.

Earlier in the day, the Iraqi military said no casualties were reported in the attack, which it said was conducted with Katyusha rockets, Reuters said.

The Iran-backed Kataib Hezbollah militia was blamed by the US for an attack on a base in Iraq last year which killed an American contractor—that led to retaliatory US strikes against it in Iraq and Syria, which prompted an assault by demonstrators on the US embassy in Baghdad. The attack on the perimeter of the embassy was a factor in US President Donald Trump in early July ordering the assassination of second most important Iranian official Major General Qasem Soleimani in an early January drone strike at Baghdad airport.

Iran responded to the assassination by firing ballistic missiles at the al-Asad air base in Iraq used by US forces. The strike did not cause any deaths of US service members and Trump decided against retaliating. However, the attack caused more than 100 American members of the military to suffer mild traumatic brain injuries.

In a statement, UK Prime Minister Boris Johnson said the attack was "deplorable".

"The Foreign Secretary has spoken to the US Secretary of State and we will continue to liaise with our international partners to fully understand the details of this abhorrent attack," he said.

Separately, also on March 11, it was announced that Iran’s aviation authority has agreed to send to Kiev for analysis black boxes from the Ukrainian airliner its forces downed just outside Tehran shortly after the attack on the US base in Iraq. Iran’s representative at the United Nations’ aviation agency informed Reuters of the move.

Farhad Parvaresh, who heads Iran’s delegation at the UN’s Montreal-based International Civil Aviation Organisation, was cited as saying Tehran’s civil aviation authority had also invited other interested countries to participate in reading the data.

The move ends a two-month stand-off over the fate of the recordings from the jet. It was shot down by the Iranian military on January 8 with the loss of all 176 people on board. It is claimed by Iranian officials that a missile gunner who had lost communications contact with his central command pulled the trigger after concluding that the aircraft was a hostile object.