Two British tank crew members have been killed by "friendly fire" from another British tank near Iraq's southern city of Basra.
The latest British casualties takes to 22 the number of British servicemen who have now been listed as dead or missing in the US-led war against Baghdad. Only two of those were killed in action.
The latest victims belonged to Britain's "Desert Rat" armoured unit and were in a Challenger tank fighting Iraqi forces west of Basra on Monday night when they were mistakenly targeted by another Challenger. Two other crew members were seriously wounded.
The Ministry of Defence identified the men as Corporal Stephen Allbutt, 35, a married father of two, and unmarried Trooper David Clarke, 19, both from central England.
"In the heat of battle there is always a risk that incidents such as this may occur," said Colonel Chris Vernon, a British military spokesman in Kuwait.
He said accidents could occur "regardless of thorough training, careful planning, excellent night-viewing equipment, and combat identification measures".
The war began on the worst possible note for Britain when 14 British troops were killed in two helicopter accidents.
Then a US Patriot missile shot down a Royal Air Force Tornado jet, killing its two-man crew.
The total death toll for British troops in the whole of the 1991 Gulf War to end Iraq's occupation of Kuwait was 24. Nine of those were killed when their armoured personnel carrier was hit by an American A10 "tankbuster" aircraft.
Time after time in the current conflict, military commanders have had to begin their daily briefings on a sombre note, paying tribute to servicemen who died accidentally.
Defence Minister Geoff Hoon said he deeply regretted the accidents but warned that in the fog of war no technological system was foolproof.
Military analysts have stressed that such accidents are inevitable.
"Unfortunately these sort of casualties are part and parcel of military operations," said Charles Heyman, editor of the military publication Jane's World Armies.
"Friendly fire" accidents seem to have become a fact of modern warfare, which is fought at lightening speed with hi-tech weaponry on often congested battlefields.
Four Canadian soldiers were killed on a training exercise in Afghanistan in April by US bombers which mistook them for Taliban fighters.
During the 1991 Gulf War, 35 of the 148 US soldiers killed in action were hit by their own side.