Three people were killed after a base hosting US and UK troops in Iraq was hit by a rocket attack.
At least 12 people were injured in the attack on the Taji military camp, north of Baghdad.
US military sources said an American soldier, an American contractor and a British soldier were killed.
Tension has been high since the US killed senior Iranian commander Qasem Soleimani in a drone strike in January.
A retaliatory Iranian strike on al-Asad – another base hosting US troops – 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 statement from the US-led coalition in Iraq and Syria confirmed that 18 rockets had struck the base and three coalition personnel had been killed.
A spokesman for the coalition said the attack happened at 19:35 local time and added that an investigation had been launched.
The Coalition @CJTFOIR confirms more than 15 small rockets impacted Iraq’s Camp Taji base hosting Coalition troops, March 11 at 7:35 p.m. (Iraq Time). Assessment and investigation ongoing, follow @OIRSpox & @SecMedCell for updates. https://t.co/oNgNfCEYG7
— OIR Spokesman Col. Myles B. Caggins III (@OIRSpox) March 11, 2020
The UK Ministry of Defence said in a statement that the British soldier who was killed was a member of the Royal Army Medical Corps.
“The service person’s family have been informed and have requested a period of privacy before further details are released,” the statement said.
UK Defence Secretary Ben Wallace called the attack a “cowardly and retrograde act”.
He said his thoughts were with the families of those killed or injured, adding: “We shall not forget their sacrifice and will ensure those who committed these acts face justice.”
No one claimed responsibility for the attack. But, in the past, Washington has accused Iran-backed factions in Iraq of carrying out similar strikes.
There have been reports of retaliatory air strikes elsewhere in Iraq, close to the Syrian border, but these have not been confirmed.