Defence Secretary Ben Wallace has vowed militia who attack Britain’s armed forces can expect a “strong response”.
Mr Wallace was commenting after the death of army medic Brodie Gillon in Iraq.
Lance Corporal Gillon, 26, was killed with two US servicemen in a rocket attack on their base Camp Taji, north of Baghdad.
America retaliated quickly with air strikes on Iranian-backed Shia militia members.
Ben Wallace Defence Secretary
Mr Wallace said: “The coalition stands shoulder to shoulder in Iraq.
“Our forces work together to help the country resist the malign activity of terrorists.
“When we and others are attacked, we reserve the right to defend ourselves.
“We support the right of the United States to defend themselves, as they have done tonight.
“We reiterate that those who seek to harm our armed forces can expect to receive a strong response.”
L/Cpl Gillon was killed while volunteering as part of the Irish Guards Battle Group during their deployment to Iraq, the Ministry of Defence (MoD) said.
Lieutenant Colonel William Leek said:
“She was a larger than life soldier who was determined to deploy on operations, help others, develop herself and gain practical experience.
“She had already achieved a great deal in her relatively short time with us and it was abundantly clear that she was destined for great things in her civilian and military careers.
“Her loss is keenly felt.
“My deepest condolences go to her family and loved ones. They are in my thoughts and prayers, and those of the wider Regimental family.”
Foreign Secretary Dominic Raab said the attack was “cowardly”.
He added: “We will defend against these deplorable acts and hold those responsible to account.”