Special Air Service Sniper Matt Tonroe, from Manchester, died last year alongside US commando Master Sergeant Jonathan J Dunbar while on an undercover mission to kill extremists.
The 33-year-old – who was embedded in Seal Team 6, the unit which killed Osama Bin Laden – became the first Briton to die fighting terrorists in war-torn Syria.
The Pentagon blamed their deaths on an improvised explosive device (IED) in a statement released days after the incident in March 2018.
But an investigation into the blast in Manbij, northern Syria, has concluded Sgt Tonroe was killed when an explosive carried by a colleague was accidentally detonated.
Special Air Service Sniper Matt Tonroe, from Manchester, died last year on an undercover mission to kill extremists
The 33-year-old died last year alongside US commando Master Sergeant Jonathan J Dunbar in the blast in Manbij during the joint mission
Investigators could not rule out the possibility that a grenade carried by another coalition soldier killed both men, according to The Morning Star newspaper.
A Ministry of Defence spokesman said: ‘Sergeant Matt Tonroe died from blast injuries caused by an explosion during a military operation.
‘It was initially believed that Sgt Tonroe was killed by enemy action, however subsequent investigation concluded that Sgt Tonroe was killed by the accidental detonation of explosives carried by coalition forces.
‘Our thoughts continue to be with Sgt Tonroe’s family and friends.’
Sgt Tonroe was born in Manchester in August 1984 and joined the Parachute Regiment just days after his 20th birthday.
He passed the Paras’ notoriously tough P Company selection course in 2005 and subsequently joined 3rd Battalion (3 Para).
Sgt Tonroe passed the Household Division and Parachute Regiment sniper course in October 2007 with flying colours.
He also served as a sniper in Helmand province in Afghanistan in 2008 and was praised for his coolness under fire by colleagues.
It is understood that his sharpshooting accounted for a number of Taliban deaths.
According to military sources, Sgt Tonroe was then promoted and attempted SAS selection, which he is said to have passed first time. He was also a fully trained parachutist.
Th explosion took place near ‘Sheikh Akil graveyard’ (pictured) in northern Syria near the border with Turkey
His commanding officer, a Lieutenant Colonel in the Special Forces who cannot be named for security reasons, described Sgt Tonroe as ‘a deeply intelligent man and one of life’s characters’.
He added: ‘‘He was a caring and considerate soul, a loving and dutiful son, and a friend to many.
‘Yet he had a steel core, served his country with pride and was a first-class soldier, proven in combat, faced risk willingly and was ever ready for more.
‘He thus died as he lived: daring and fearless in duty. We mourn his loss dearly, are proud to have known him and will honour him by continuing this fight.’
Sgt Tonroe was survived by his mother Michelle, brother Alex and girlfriend Olivia.
US Special Forces soldier – Master Sergeant Jonathan Dunbar, 36, from Austin, Texas – was also killed when the device exploded near Manbij’s Sheikh Akil cemetery.