LONDON (AP) — Officials say a British special forces soldier who died fighting the Islamic State group in Syria was killed by friendly fire, rather than in a roadside bomb as previously believed.

Sgt. Matt Tonroe died in March 2018 alongside U.S. commando Master Sergeant Jonathan J. Dunbar while on a joint operation in Manbij, northern Syria, with American special forces. The Pentagon had said they died from improvised explosive devices.

But investigators have concluded that Tonroe, 33, was killed by an explosive carried by a colleague.

Britain's Defense Ministry said Saturday that while "it was initially believed that Sgt. Tonroe was killed by enemy action," a subsequent investigation concluded he was killed by "the accidental detonation of explosives carried by coalition forces."