Former Bosnian Serb army chief Ratko Mladic's defence case opened at the Yugoslav war crimes court with one of his officers insisting his forces acted in self-defence during the bloody siege of Sarajevo.

Mile Sladoje told the three-judge panel at the International Criminal Tribunal for the former Yugoslavia that his troops "never were snipers" during the 1990s siege in which 10,000 people died.

Mr Mladic faces charges of genocide and crimes against humanity.

"All our activities (in Sarajevo) were defence activities," Mr Sladoje said in a statement read by Mr Mladic's lawyer Miodrag Stojanovic before questioning began.

"There were standing orders, fire could only be returned in response to enemy fire," said Mr Sladoje, an assistant logistics commander in the Bosnian Serb Army.

He was saluted by Mr Mladic as he walked into the courtroom.

Dubbed the "Butcher of Bosnia", Mr Mladic, 72, faces 11 charges ranging from hostage-taking to genocide for his role in Bosnia's brutal 1992-95 conflict following the break-up of the former Yugoslavia.

Around 100,000 people were killed and 2.2 million others left homeless in the brutal conflict, which included some of the worst atrocities committed on European soil since World War II.

Mr Mladic is charged with involvement in the slaughter of almost 8,000 Muslim men and boys at Srebrenica in July 1995 and the 44-month siege of the Bosnian capital Sarajevo.

He is accused of waging a "campaign of terror" against Sarajevo's civilians by indiscriminate shelling and employing snipers during the siege, in which thousands of civilians died.

But Mr Sladoje, referring to an incident in Sarajevo when a teenage girl was shot by a sniper, denied there were snipers among his troops or that they had sniper weapons.

"We had normal infantry weapons, we never had snipers or such rifles," he told the judges.

Mr Mladic, dressed in a black suit, black tie and white shirt, listened attentively as Mr Sladoje spoke.

At Srebrenica, Mr Mladic's forces are accused of overrunning lightly armed Dutch UN troops protecting the supposedly safe enclave, before murdering the men and boys and dumping their bodies into mass graves.

He has also been charged for taking hostage a group of more than 200 United Nations peacekeepers during the conflict, keeping them in strategic locations as "human shields" against NATO air strikes.

Presiding Judge Alphons Orie has given Mr Mladic's lawyers 207 hours to question witnesses.

That is the same amount of time given to the prosecution, who finished its case earlier this year, the ICTY said in a statement.