Chief UN war crimes prosecutor Carla Del Ponte has indicted three more Bosnian Serbs for taking part in the Srebrenica massacre in 1995.

Mrs Del Ponte handed the sealed indictments over to the Yugoslav authorities during a visit to Belgrade.

The UN war crimes tribunal later revealed the identities of the three accused - Drago Nikolic, Vujadin Popovic and Ljubisa Beara - and said they were charged with genocide, crimes against humanity and war crimes.

It is a fact that we have so many fugitives who are under arrest warrant and who are not arrested

Carla Del Ponte

The men are accused of killing Muslim prisoners and forcing tens of thousands of women and children out of Srebrenica, which at the time was a UN-protected enclave.

According to the indictment, the three were also part of a scheme "to capture, detain, summarily execute by firing squad, bury, and rebury thousands of Bosnian Muslim men and boys aged 16 to 60 from the Srebrenica enclave".

The UN tribunal has already convicted a Bosnian Serb general, Radislav Krstic, for the mass killings in the town - in which more than 8,000 Bosnian Muslims are thought to have died.

Improving co-operation

Mrs Del Ponte was in Belgrade for talks with Yugoslav Foreign Minister Goran Svilanovic and Serbia's Prime Minister Zoran Djindjic.

Ratko Mladic is believed to be hiding in Serbia

The talks were aimed at speeding up co-operation between Belgrade and the UN tribunal, notably on the extradition of war crimes suspects believed to be in hiding in Yugoslavia.

A statement issued after the talks said Mrs Del Ponte "expressed dissatisfaction" over Belgrade's lack of co-operation.

"It is a fact that we have so many fugitives who are under arrest warrant and who are not arrested," she said.

In the past Mrs Del Ponte has particularly complained that former Bosnian Serb commander Ratko Mladic - whom she insists is hiding in Serbia - still remains at large.

Search for Mladic

During her last visit to Belgrade in July, Mrs Del Ponte urged Yugoslav officials to step up the hunt for Mr Mladic.

But the Yugoslav authorities say they do not know where he is.

Slobodan Milosevic is on trial in The Hague

Mr Mladic has been indicted by the UN tribunal for allegedly ordering and carrying out the siege of Sarajevo during the 1992-1995 Bosnian war, as well as the massacre in Srebrenica.

Along with Mr Mladic, Bosnian Serb leader Radovan Karadzic also tops the list of the UN tribunal's most wanted suspects.

Mr Karadzic is believed to be hiding in the Serb-controlled part of Bosnia.

Yugoslavia has been under constant pressure from the international community to hand over all war crimes suspects, since last June's extradition of former president Slobodan Milosevic.

Mr Milosevic is currently on trial for war crimes in Bosnia, Croatia and Kosovo during the 1990s.

Belgrade has so far failed to apprehend any of the suspects still at large, despite passing legislation earlier this year to allow the extradition of Yugoslav citizens to the court.

Six Serbs voluntarily surrendered in the spring.