Bosnian Serb officials have acknowledged for the first time that their security forces carried out the massacre of up to 8,000 Muslims at Srebrenica, according to an investigative report published Friday.

An official commission examining Europe's worst massacre since World War II "established participation of [Bosnian Serb] military and police units, including special [police] units" in the deaths, international administration spokesman Vedran Persic said, quoting from the commission's report.

At the height of the 31/2-year Bosnian war, Serbian troops overran a U.N.-declared safe zone in Srebrenica and slaughtered up to 8,000 Muslim men and boys.

The Bosnian Serbs have long been blamed for the 1995 killings, which the U.N. war crimes tribunal has declared an act of genocide. But until now, no Serbian official has clearly acknowledged that Bosnian Serbs were the perpetrators.

"In July 1995, several thousand Muslims were liquidated in a way that represents grave violations of international humanitarian law," said Persic, quoting from the report. Persic is a spokesman for Paddy Ashdown, Bosnia's international administrator.

U.N. and Muslim experts have found the remains of about 5,000 of the victims in mass graves across eastern Bosnia and find new remains every month. The fate of the others is still unknown. Nearly 1,200 Srebrenica victims have been identified through DNA analysis.

Dutch peacekeepers charged with protecting the Srebrenica enclave failed to prevent the massacre. The Dutch government acknowledged the failure and resigned in April 2002.

Radovan Karadzic, the Bosnian Serb wartime leader, has been indicted by the war crimes tribunal for genocide in connection with the Srebrenica massacre, along with his top wartime general, Ratko Mladic. Both remain at large.

The 1992-1995 war claimed about 250,000 lives. About 20,000 others are missing and presumed dead. The remains of about 18,000 victims from different ethnic groups have been exhumed from more than 300 mass graves across the country.

The Srebrenica Commission was formed last year by Ashdown to investigate who was involved in the massacre and where victims' bodies were buried. It is composed of Bosnian Serb judges and lawyers, a victims' representative and an international expert.

The report said the perpetrators of the massacre "undertook measures to cover up the crime by moving the bodies" to other locations, Persic said.

The Bosnian Serbs had long refused to acknowledge that their forces committed the worst civilian massacre in Europe since World War II. The work of the Srebrenica Commission, too, initially was obstructed by some of its members and authorities who refused to provide information.

Only after Ashdown fired several Bosnian Serb officials and threatened others with dismissal was information made available.

Under the 1995 peace accord that ended the war, Ashdown has the power to impose laws and to fire officials who fail to comply with the peace process. The same agreement also divided postwar Bosnia into two mini-states, a Serbian republic and a Muslim-Croat federation.

Persic said Ashdown welcomed the report, saying that "a dynamic of obstructionism on war crimes issues is being replaced by a dynamic of greater cooperation" on the part of Bosnia's Serbs.