A spokesman for British forces in the Kosovan capital, Pristina, said the farmers had arranged for the escorts to begin on Saturday morning. They said they felt under threat while gathering the harvest.

UK military police in Kosovo have promised to hunt down those responsible for the killings. The Serbs were killed only hours before the protection was due to commence.

General Sir Mike Jackson, head of the Nato-led peacekeeping force, said investigators would "leave no stone unturned" after the "cowardly act of brutal and cold murder".

The investigations, led by a British team, are being carried out according to English law.

Police suspect that the Serbs were killed in a revenge attack by ethnic Albanians.

Late on Friday, British troops patrolling a sector 25km south of the capital discovered 13 bodies in a field close to a combine harvester, half an hour after hearing gun shots. The 14th body was found on a tractor nearby.

Gen Jackson said the events had reinforced his determination and those of his soldiers to bring peace to Kosovo.

"We have to break the cycle of violence. This cannot be a catalyst for further revenge or blood letting," he said.

Horrendous crime

The mass killings are one of the worst single acts of violence since Nato troops moved into Kosovo in June.

Ian Seraph, a spokesman for British peacekeepers in the area, said the civilians had been shot with automatic weapons. "It is horrendous crime that must be investigated," he said.

Lt Col Robin Hodges, one of the first soldiers to arrive on the scene, called for calm and restraint. He said: "These killings are particularly terrible coming as they do when peace was beginning to return to Kosovo."