The trial of former Bosnian Serb army chief General Ratko Mladic, charged with crimes against humanity, has been suspended for six months after prosecutors failed to reveal thousands of documents to Mladic's defence team.

Judge Alphons Orie announced the delay at the Yugoslav war crimes tribunal at The Hague because of "significant disclosure errors" by UN prosecutors, who were supposed to share all evidence before the deadline of November 2011.

He said judges were still scrutinising the "scope and full impact" of the error and adjourned the trial for six months.

Millions of pages contained in tens of thousands of documents were not disclosed to the defence, according to court officials.

In view of the oversight, Mladic's attorney asked for a six-month delay.

Court spokeswoman Nerma Jelacic told AP that the missing material focused on witnesses whomthe prosecutionwanted to call to testify before July.

The former Bosnian Serb army chief faces 11 charges, including two counts of genocide, as well as extermination, murder, inhumane acts and deportation, is believed to be responsible for the worst atrocities in Europe since the Nazi era.

Over two nights in July 1995, the Bosnian Serb army shot 8,000 Muslim men and boys in and around the town of Srebrenica.

"In a period of only five days, from 12-16 July, 1995, the armed forces of [Bosnian Serb leader] Radovan Karadzic and Ratko Mladic expelled the civilian population of Srebrenica and murdered over 7,000 Srebrenica men and boys," prosecutor Peter McCloskey said. Other estimates range up to 8,000 dead.

Defiant and smiling, Mladic clapped his hands and attempted a thumbs-up sign as he arrived in the courtroom at The Hague.

He made eye contact with Munira Subasic, a woman who lost 22 relatives to Bosnian Serb military forces, and ran his hand across his throat.

Prosecutor Dermot Groome told the court that the war criminal had the goal of ethnically cleansing Bosnia. The world watched in disbelief that, in neighborhoods and villages within Europe, a genocide appeared to be in progress, he said.

For years after the war, Mladic managed to evade justice with the help of Serbian army comrades and the Serbian state. He was finally arrested last year after the election of reformist president Boris Tadic.