A member of the British Army's elite Special Air Service who died alongside a U.S. special operator during a counter-ISIS operation in Syria last year was killed by “the accidental detonation of explosives carried by coalition forces” rather than an enemy IED as the Pentagon initially claimed, according to an investigation by the UK Ministry of Defense.

British Army Sgt. Matt Tonroe was killed in March 2018 during a joint operation with U.S. special operations forces near Manbij, Syria.

U.S. Army Master Sgt. Jonathan J. Dunbar, a member of the service's legendary Delta Force, was also killed in the incident.

The Pentagon stated that the joint UK-US force was “conducting a mission to kill or capture a known ISIS member when they were struck by an improvised explosive device,” as spokesman Marine Maj. Adrian Rankine-Galloway told Task & Purpose at the time.

But while the UK MoD confirmed that while Tonroe “died from blast injuries caused by an explosion during a military operation,” that explosion was actually the result of friendly action rather than an ISIS IED.

“It was initially believed that Sgt. Tonroe was killed by enemy action,” the MoD said in a statement. “However subsequent investigation concluded that Sgt. Tonroe was killed by the accidental detonation of explosives carried by coalition forces.”

When reached by Task & Purpose the Office of the Secretary of Defense referred questions to U.S. Special Operations Command, which did not immediately respond.

Before his selection for the Special Air Services Regiment, Tonroe was a sniper assigned to he 3rd Battalion, Parachute Regiment (3 PARA). According to the Guardian, he spent time attached to SEAL Team 6.

This is a developing story and will be updated with new information as it becomes available