UN prosecutors open their case Monday against Bosnian Serb ex-military chief Ratko Mladic before the Yugoslav war crimes court, with their first witness to testify on how he survived a mass execution in 1992.

Elvedin Pasic was a 14-year-old Muslim boy when Bosnia's bitter war broke out that year. When it ended in 1995, some 100,000 people had been killed and 2.2 million others left homeless.

Now 34, Pasic "will describe the destruction and damage to residential property, attacks on villages (and) the persecution of non-Serbs," prosecutors said in a witness list before the court.

Pasic will recall how he was separated from other men in his family and subsequently "survived the execution of around 150 persons in November 1992 in the village of Grabovica," in northern Bosnia.

His testimony will be followed by that of UN advisor David Harland, who will describe the siege of Bosnian capital Sarajevo, where 1,000 shells landed on average each day between 1993 and 1995, with the exception of lulls during a 1994 cease-fire.

Also among the first witnesses to testify against Mladic before the International Criminal Tribunal for the former Yugoslavia, is Eelco Koster, a former Dutch UN peacekeeper during Bosnia's 1995 Srebrenica massacre.

The murder of almost 8,000 Muslim men and boys in mid-July 1995 after Bosnian Serb troops overran some 450 UN blue helmets guarding the "protected" enclave in the country's east is the worst single atrocity committed on European soil since World War II.

Mladic, now 70, has been indicted on 11 counts of genocide, war crimes and crimes against humanity for his role in the Balkan country's war.

Former Bosnian Serb political leader Radovan Karadzic is already on trial before The Hague-based ICTY. Both men are believed to be the main players in a joint criminal plan to rid multi-ethnic Bosnia of Croats and Muslims.

Dubbed the "Butcher of Bosnia", Mladic faces charges relating to the tragedy at Srebrenica and the terrorising of Sarajevo's citizens through a 44-month shelling and sniping campaign which killed 10,000.

Prosecutors also hold him responsible for taking some 200 UN peacekeepers hostage to use them as human shields.

Mladic allegedly also ordered his troops to "cleanse" Bosnian towns, driving out Croats, Muslims and other non-Serb residents.

An indicted war criminal, he spent 16 years on the run until May 2011 when he was found and arrested at a relative's house in Lazarevo, northeastern Serbia and flown to a prison in The Hague a few days later.

He has pleaded not guilty to the charges.

Proceedings have been on hold since a day after the trial started on May 16 because of "irregularities" in the transfer of prosecution documents to the defence.

On May 31 lawyers defending Mladic asked for a six-month extension to the trial's delay, but judges set Monday as the day for the trial to resume.