The team leader, Helena Ranta, said there was a possibility the bodies had been tampered with during the period they were not under international supervision.

She said she would be taking the matter up with the Yugoslav authorities.

"The problem as we see in this particular case it is very difficult to reconstruct the chain of custody of the bodies from the site to the mosque, from the mosque to the department of forensic medicine," she said.

"So there is a possibility of contamination and, of course, we have to bear in mind there is also a possibility of fabrication of evidence. This will be discussed with Yugoslav authorities."

The head of the Organisation for Security and Co-operation in Europe (OSCE) has described the killings as a civilian massacre, but the Serbs say those who died were rebels killed in battle.

The Yugoslav health minister, Miodrag Kovac, said the post-mortems carried out so far showed the victims had been shot from a distance.

Autopsies may be reviewed

Ms Ranta's team, working on behalf of the OSCE, is conducting autopsies with local forensic experts and a team from Belarus.

She said that before she joined them, a Yugoslav forensic team had performed autopsies on 16 bodies.

She said her team would review videos of those autopsies, X-ray the bodies and if necessary re-examine them.

Her team had completed autopsies on 15 bodies which had not been dealt with before, she said, adding that nine remained to be examined.

She could not say when the work might end because of the need to translate all the paper work.