Names and details of the units alleged to be carrying out "the worst ethnic cleansing this century" were revealed at a Ministry of Defence (MoD) news conference on Thursday.

During the briefing, Foreign Secretary Robin Cook warned Serbia's President Slobodan Milosevic that his army was running out of fuel and he was running out of time.

Major General John Drewienkiewicz, the former head of the OSCE's Kosovo verification mission, gave moving details of the refugee exodus from Kosovo.

Maj Gen Drewienkiewicz: "Ethnic Albanians have been told 'Don't come back or you'll be shot'."

He said there was evidence that ethnic Albanians had been beaten, robbed, raped and murdered all over the Serbian province. He added that there were reports of a mass grave near Prizren.

Maj Gen Drewienkiewicz said thousands of Kosovar Albanians had fled their homes and he described one refugee column, seen heading towards the Macedonian border, as looking like a "scene from Schindler's List".

The areas outlined in red is where 'ethnic cleansing' has been reported

MoD official Julian Moir gave details of the Serbian chain of command which is allegedly behind the war crimes in Kosovo.

Among those he accused were:

• Serbia's Interior Minister Vlajko Stojilkovic

• The head of the Department of State Security, General Radomir Markovic.

• Frankie Simatovic, head of the Department of State Security's operations wing.

• Major General Circic, head of the Serbian secret service (RDB) and responsible for "black" operations.

• Maj Gen Lukic, head of the ministry of interior's armed gendarmerie.

• Lt Col Gen Stefanovic, head of the interior ministry's PJP police assault troops in Kosovo. The PJP are the backbone of Serbian control in Kosovo and have allegedly responsible for many of the atrocities.

UK Foreign Secretary Robin Cook: "Many Serbian units in Kosovo are running low on fuel"

Mr Simatovic was said to have a "good pedigree" of organising paramilitary groups in Bosnia-Herzegovina and Kosovo which had carried out atrocities.

Mr Moir said he was a conduit between the state and irregular militias who were believed to be carrying out the war crimes. He said he was a "shadowy" figure and there was no picture of him.

Among the forces under Mr Simatovic's control are believed to be the JSO, a 500-strong group recruited from the Serbian special forces.

Mr Moir said the JSO wore red berets and were frequently masked.

He said they worked in bands of 15-20 and were "by any standards well-trained, well-motivated and very, very dangerous".

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Mr Moir said they were also believed to be acting as Mr Milosevic's "Praetorian Guard".

He said the JSO worked "hand in glove" with the Serbian anti-terrorist squad, SHA, which is 400-strong.

Mr Cook said they were sharing all British intelligence information on the alleged war criminals with the judge in charge of the war crime tribunal in The Hague.

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At one point he was asked how Nato could consider negotiating with Mr Milosevic when he was one of those they considered a war criminal.

Mr Cook said it would be up the war crimes tribunal to decide whether he was legally responsible for atrocities in Kosovo.