The American-based Human Rights Watch said dozens of Serbs had been killed or abducted in revenge attacks - and many more had been beaten or robbed - since the Yugoslav forces withdrew in June.

It said Serbs and gypsies had been the victims of "direct and systematic efforts" by the Kosovo Albanians to force them to leave their homes.

Fred Abrahams of Human Rights Watch

The Hungarian-based European Roma Rights Centre also reported the intimidation suffered by gypsies at the hands of the Kosovo Albanians.

Kosovo Albanians say that once the Serbs forced them out of their homes during the Nato air war, it was usually the gypsies who moved in to loot their possessions.

The Kosovo Albanians are now taking their revenge on both communities, say the reports.

Call for international police

The human rights groups said efforts by the Nato-led peacekeepers to stop the violence were ineffective, and called for the urgent deployment of an international police force in Kosovo.

K-For defends its record in Kosovo: "Actually we have a rigid order here"

Since the publication of the report, Nato peacekeepers say they have arrested five Kosovo Albanians for the abduction and murder of a Serb man, and detained two others for the killing of an elderly Serb woman.

Nato officers say the murder rate in Kosovo has dropped to half of what it was six weeks ago, and that this is a measure of the peace-keeping operation's success.

But the UN has still not deployed an international police force.

Human Rights Watch says the frequency of abuses against Serbs and Roma is a consequence of this lack of a police force.

Murder of old women

The human rights group says that more than 160,000 Serbs have fled Kosovo since Nato arrived, along with significant numbers of gypsies.

Roma live in fear

The organisation's report highlights a series of killings, including the murders of 14 Serb farmers at Gracko last month.

It also documents less well-known cases, such as that of 77-year-old Marica Steminkovic, and 63-year-old Panta Philipovic. The two women had lived in the town of Prizren for decades and decided to stay when other Serbs fled the city.

Within days, Human Rights Watch says, uniformed KLA members began appearing at their homes demanding money and arms.

After repeated visits, both women were found with throats cut, Marica Steminkovic almost decapitated.