Bosnian Serb authorities offered details of six previously undisclosed mass graves in the town of Srebrenica on Friday, their first step in cooperating with a commission investigating the worst civilian massacre (search) in Europe since World War II (search).

Bosnian Serb military and police officials submitted details of the graves to the chairman of the commission studying the massacre of up to 8,000 Muslim men and boys in 1995.

The Muslims were massacred when Serbs overran the eastern Bosnian enclave during the 31/2-year war in the former Yugoslav province.

"The mass graves are located in the wider Srebrenica region and we have already been to the sites," commission chair Milan Bogdanic told The Associated Press.

He refused to disclose the exact location of the mass graves or give an estimate of the number of victims buried in each one.

The disclosure came after Bosnia's international administrator, Paddy Ashdown, ordered Bosnian Serb authorities to cooperate — or lose their jobs.

When authorities at first failed to act, Ashdown used powers granted under the peace plan that ended Bosnia's 1992-1995 war to fire Gen. Cvjetko Savic, the chief of staff of the Bosnian Serb army, and Dejan Miletic, a Bosnian Serb official responsible for cooperation with the U.N. war crimes tribunal in The Hague, Netherlands.

Ashdown also told the president and the prime minister of the Serb republic that they would be held personally responsible if they failed to make it possible for the commission to complete its work by June.

With the deadline looming, the Bosnian Serb authorities began to act.

Under the peace accord that ended the war, Ashdown has the power to impose laws and fire officials who fail to comply with the peace process. The same agreement also divided postwar Bosnia into two mini-states, a Serb republic and a Muslim-Croat federation.

The new information "is a clear sign that Bosnian Serb officials are starting to cooperate with the commission," said Vedran Persic, Ashdown's spokesman.

The information on the graves is significant because thousands of Muslims are still missing.

Bosnian Muslim officials claim that up to 20 mass graves are still undisclosed, and the failure to address the question has stalled Bosnia's efforts to move past the war and toward the West.

The Bosnian Serbs have also been under pressure to acknowledge that their forces committed atrocities in Srebrenica and to name the perpetrators.

The Srebrenica investigation commission includes Bosnian Serb judges and lawyers, a representative of the victims' families and an international expert.