A taskforce from the international agency is now in Kosovo to assess the environmental impact of both the prolonged bombing raids and any actions taken by Serb forces before their withdrawal.

And experts have warned that the graves uncovered by K-For peacekeeping troops could be an additional health hazard for villagers returning to their homes.

Dr Philip Rushbrook, who is co-ordinating the taskforce, said: "We are worried about these graves and about other burial sites in Kosovo.

"We are aware of instances where water courses have been affected by large numbers of bodies in rough, unconstructed graves."

Similar problems in Bosnia

WHO experts found similar problems in Bosnia following the discovery of mass graves there after fighting had ended.

If the water supply comes into contact with decomposing bodies, it could cause outbreaks of disease in communities which rely on a single stream.

However, the graves are not the only concern for the WHO team.

Chemical leakage

Dr Rushbrook said that chemicals leaking after the Nato bombardment could also cause problems, and that the taskforce would also investigate fears over pollution left by Nato weapons constructed using radioactive materials.

Clean drinking water is a vital requirement for the returning refugees

It also plans to help with the reconstruction of adequate sanitation for returning refugees, and ensure that basic health facilities can be provided.

He said: "Some of the most common communicable diseases come from these environmental problems."