The soldiers were travelling in an armoured vehicle that hit a mine near Mrkonjic Grad, in an area which is due to be returned from Croat to Bosnian Serb control under the Dayton peace agreement.
Lieutenant-Colonel David Shaw, an Army spokesman in Gornji Vakuf, said attempts to get to the vehicle were hampered by difficult weather and by the possibility of other, unmarked land mines.
The men's names and units were not made immediately available. Col Shaw said three men had been travelling with a second British armoured vehicle when the explosion occurred. The incident happened in a volatile area, nicknamed the Anvil.
Until yesterday, the British were delighted with the success of their operation, supervising the withdrawal of Croat forces from the area, ensuring the withdrawal of armed troops from the zone of separation between Croats and Serbs and marking all the minefields.
There are estimated to be up to 6 million mines scattered around Bosnia. Although the former warring factions have tried to identify as many as possible, many unmarked minefields remain. Nato engineers believe no more than 30 per cent have been marked.
The British armoured vehicles hit yesterday were in an area where the Nato-led peace force, I-For, did not believe there were mines. Part of the peace agreement requires the parties to hand over maps of where they put mines.
The British unit in the area is 4 Armoured Brigade, of Gulf war fame. Its troops come from the Second Battalion The Light Infantry and the Royal Fusiliers, with support from the Royal Artillery and the Royal Logistic Corps. The peace implementation force will eventually total 60,000 troops. Britain has about 13,000 men and women taking part.
Up to yesterday, 35 soldiers of the Nato force had been injured since the troops began arriving in Bosnia, most of them in mine accidents. Four soldiers had died, including one British soldier, who killed himself at Christmas.
Two Portuguese soldiers and one Italian were killed in Sarajevo last week when a piece of ordnance which one of them brought in from the field exploded in their sleeping quarters. An American officer was grazed in the neck yesterday by a bullet which struck him as he walked in the grounds of a Sarajevo hotel complex used by Nato as headquarters for its ground force commander. Nato said he "was shot in an apparent sniper incident".
French Nato forces reported two separate shooting incidents on Saturday in the area, but could not identify the firing points or the targets.
Professor David Southall, head of the medical charity Child Advocacy International, and a member of the UK Working Party on Land mines, said: "I hope this will add weight to the evidence that no country in the world should making or exporting weapons that are effectively a form of terrorism.
"The people of Bosnia will have to live with unmarked mines for decades. They kill and injure more children than adults.
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