A British soldier and two Americans have been killed in a rocket attack on Camp Taji in Iraq.
Around 12 others were injured in the attack which happened on Wednesday.
No group has claimed responsibility for the attack, but it has been suggested Iranian-backed Shia militia groups could have been involved.
Kata'ib Hezbollah was behind a rocket attack on a military base in Kirkuk in December that killed a US contractor, prompting American military strikes in response.
Yesterday's attack happened on the same date as the birthday of Iranian general, Qassem Soleimani, who was killed by US forces in January.
The UK soldier who died was named this evening as Lance Corporal Brodie Gillon.
She was a reservist who had volunteered to be part of the Irish Guards Battle Group during their deployment to Iraq.
Defence Secretary Ben Wallace called the attack a "cowardly and retrograde act".
"The men and women of the UK Armed Forces are in Iraq to help that country establish stability and prosperity," Mr Wallace said.
"The people that did this are not friends of Iraq.
"We shall not forget their sacrifice and will ensure those who committed these acts face justice."
Prime Minister Boris Johnson tweeted that his "thoughts go out to their loved ones at this extremely difficult time".
Meanwhile, Foreign Secretary Dominic Raab condemned the "cowardly" attack on the Taji air base and said the UK and its allies would "hold those responsible to account".
General Kenneth F McKenzie, Head of US Central Command, suggested "Shia militia groups" could be behind the attack.
"While we are still investigating the attack, I will note that the Iranian proxy group, Kata'ib Hezbollah, is the only group known to have previously conducted an indirect fire attack of this scale against US and coalition forces in Iraq," he said.
Gen McKenzie added that recent events "indicate the Iran regime’s desire to continue malign activities that threaten lives".
Colonel Myles Caggins, a US military spokesman in Iraq, earlier stated that "more than 15 small rockets" had hit Camp Taji, while retweeting images appearing to show a missile platform vehicle found south of Iraq's the Rashidiya region.
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
Minister for Defence People and Veterans, Johnny Mercer, told Forces News that the attack was a "tragedy" and a "timely reminder of what we ask our service people to do".
"They’re extraordinary people and sometimes they pay the ultimate price," Mr Mercer said.
"My thoughts are very much with this individual’s family and friends at what is a really, really difficult time".
WATCH: Johnny Mercer tells Forces News the soldier's death is a 'tragedy'.
The United Nations has condemned the incident and urged the Iraqi government to "hold perpetrators accountable and prevent future attacks".
In January, the Camp Taji was the target of a "small attack", with none of the 200 British personnel at the base being injured.
What is Camp Taji?
Around 400 UK military personnel are currently stationed in Iraq across several sites, including Camp Taji.
The base, located just north of Baghdad, has been used as a training base for a number of years.
It covers 13 square miles and is located northwest of Baghdad in an area called Tarmiya.
The site is home to hundreds of coalition troops, including a British team training Iraqi personnel.
Cover image: Library photo of Camp Taji in Iraq.