The BBC's Gillian Sharpe in the Hague: "Arguably the most important defendant the Tribunal has custody of"

General Krstic - the highest-ranking Serb military officer to be tried in the Hague - is accused of having played a key role in the execution of thousands of Muslim men after the fall of the UN enclave of Srebrenica.

Srebrenica was overrun by Bosnian Serb militia in 1995 and as many as 8,000 Muslim men are believed to have been killed.

The general is indicted as the Commander of the Drina Corps of the Bosnian Serb Army, which led the campaign from July to November.

Women of Srebrenica were allowed to go, their menfolk disappeared

General Krstic, 50, was allowed to remain seated as he entered his pleas. His lawyer said he was suffering from serious injuries which made it difficult for him to stand up.

Asked how he felt, General Krstic said: "As well as can be expected on the whole, but I am tired after the arrest. Exhausted."

He also complained that there was no heating in his high-security UN cell and that he was receiving no therapy for his injured leg.

He lost part of his right leg, reportedly after stepping on a mine in 1994.

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No trial date has yet been announced. If convicted, he faces a maximum sentence of life imprisonment.

Prosecutor Brenda Hollis said she would likely call between 50 and 70 witnesses at the trial, which is expected to last for months.

High-profile associates

General Krstic was arrested last week by Nato-led peacekeeping forces in the north of the Bosnian Serb Republic.

He faces charges brought both in respect of his personal involvement in the alleged crimes, and in respect of his responsibility for the actions of soldiers under his command.

Charges against the general include:

• Complicity to commit genocide
• Extermination, a crime against humanity
• Murder, a crime against humanity
• Violation of the laws or customs of war
• Persecution, a crime against humanity.

General Krstic is believed to be a close associate of former Bosnian Serb leader, Radovan Karadzic, and his General, Ratko Mladic - the tribunal's top two suspects.

The two are also indicted for genocide at Srebrenica, but have so far avoided arrest.

General Krstic is said to have been seen with General Mladic while men were being separated from women near the town.