Former Bosnian Serb military commander Ratko Mladic has gone on trial at a UN tribunal on 11 charges of genocide, crimes against humanity and war crimes.

The ailing 70-year-old's appearance at the Yugoslav war crimes tribunal marks the end of a long wait for justice for survivors of the 1992-95 war that left 100,000 people dead.

Mladic gave a thumbs-up and clapped to supporters in the public gallery of the court at The Hague, Holland, as the trial got under way 20 years after the opening shots of the Bosnian War.

Munira Subasic, who lost 22 family members in the 1995 Srebrenica massacre, was among a group of relatives of war dead heading into the courtroom to face Mladic.

The 65-year-old said she wanted to look him in the eye "and ask him if he will repent for what he did".

The trial is a landmark for the UN court and international justice - Mladic is the last suspect from the Bosnian War to go on trial there.

Mladic, wearing a suit and tie, occasionally wrote notes and showed no emotion as prosecutors began outlining his alleged crimes.

Presiding Judge Alphons Orie said at the outset that the court was considering postponing the presentation of evidence, due to start May 29, due to "errors" by prosecutors in disclosing evidence to the defence.

Prosecutor Dermot Groome said he would not oppose a "reasonable adjournment".

Mr Groome opened his statement by focusing on the plight of a 14-year-old boy whose father and uncle were among 150 men murdered by Bosnian Serb forces in November 1992.

He said Mladic's forces continued such killings through to 1995, when they massacred 8,000 Muslim men in the Srebrenica enclave.

"By the time Mladic and his troops murdered thousands in Srebrenica ... they were well-rehearsed in the craft of murder," Mr Groome told the court.

He showed judges video of the aftermath of a notorious shelling of a market in Markale, in the Bosnian capital Sarajevo, that killed dozens of people.

He said all the attacks were part of an "overarching" plan to ethnically cleanse parts of Bosnia of non-Serbs.

Prosecutors will show evidence "beyond reasonable doubt the hand of Mr Mladic in each of these crimes", Mr Groome said.

Mladic has refused to enter pleas, but he denies wrongdoing, saying he acted to defend Serbs in Bosnia. If he is convicted, he faces a maximum sentence of life imprisonment.