A base hosting US and UK troops in Iraq has been hit in a rocket attack, US military officials say.
The attack was on the Taji military camp north of Baghdad.
The US sources said an American soldier, an American contractor and a British soldier were killed but this has not been officially confirmed.
Tension has been high since the US killed senior Iranian commander Qasem Soleimani in a drone strike in Baghdad on 3 January.
A retaliatory Iranian strike on al-Asad, another base hosting US troop on 8 January left more than 100 soldiers suffering from traumatic brain injuries (TBI).
However, both Iran and the US appeared then to want to draw a line under the matter and there have been no major flare-ups since.
A spokesman for the US-led coalition in Iraq and Syria, Col Myles Caggins, confirmed that a number of rockets had struck the base at 19:35 local time (16:35 GMT) on Wednesday.
He said an investigation had been launched.
he UK Ministry of Defence said of the latest incident: “We can confirm we are aware of an incident involving UK service personnel at Camp Taji, Iraq. An investigation is under way, it would be inappropriate to comment further at this time.”
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.
There have been reports of retaliatory air strikes elsewhere in Iraq, close to the Syrian border, but these have not been confirmed.
Earlier this year, Iraq’s parliament passed a resolution calling for all foreign troops to leave the country.
It followed the killing of Soleimani, which marked a major escalation in tensions between Tehran and Washington. Soleimani spearheaded Iranian military operations in the Middle East and was regarded as a terrorist by the US.
Some 5,000 US soldiers are in Iraq as part of the international coalition against the Islamic State (IS) group.
The UK, meanwhile, has 400 troops based in the Middle East and works alongside US forces in the region.