The officials, who cautioned the death toll may rise given the severity of some of the injuries, said it was too soon to assign blame.

US Secretary of State Mike Pompeo spoke with British Foreign Secretary Dominic Raab and they “underscored that those responsible for the attacks must be held accountable,” the State Department said.

The US-led military coalition in Iraq said in a statement that 18 107 mm Katyusha rockets struck the base and suggested they may have been fired from a truck, Reuters reported.

It confirmed three personnel were killed and about a dozen wounded but declined to disclose the nationalities of the casualties or offer any other identifying information.

“The attack is under investigation by the Coalition and Iraqi Security Forces,” the US-led coalition said.

The State Department readout of the call with Raab said that there had been American, British and other casualties in the attack, but it did not provide details.

British Prime Minister Boris Johnson issued a statement condemning the attack and added that Raab had spoken with Pompeo.

“We will continue to liaise with our international partners to fully understand the details of this abhorrent attack,” Johnson said, without confirming British casualties.

Meanwhile, Iraqi President Barham Salih condemned the attack on the Taji military camp, the state news agency said on early Thursday.

‘This aggression targets Iraq’s security,’ Salih’s office said in a statement, stressing the need for an investigation into the attack.

Reporter’s code: 50101