Mr Ocalan has been charged with treason and attempting to divide the state by force. If convicted, he faces a mandatory death penalty.

In excerpts from the trial shown on state-run television, Mr Ocalan told the court: "I share the grief of the families of the martyrs, and I promise here that from now on I will work for the establishment of peace.''

Tom Kankinen in Turkey: Mr Ocalan said he was ready to serve the state in order to work for peace

Pleading to be spared the death penalty, Mr Ocalan said: "For peace and brotherhood I am ready to serve the Turkish state, and I believe that for this end I must remain alive.''

The hearing began after the court rejected a request by Mr Ocalan's lawyers to adjourn the trial. They say they have been hampered in preparing his defence.

Heavy security around Imrali island

Security has been intensified on and around Imrali island, which lies in the Sea of Marmara, 70km south of Istanbul. Mr Ocalan is the only inmate at the prison.

Chris Morris in Turkey: Conciliation is not on the agenda

Heavily-armed troops are maintaining a military exclusion zone around the island; warships and helicopters are also on patrol. During the trial, Mr Ocalan will sit inside a specially-built bullet-proof glass cage.

Mr Ocalan's arrest and trial has polarised opinion in Turkey.

His supporters were outraged when he was captured in February and brought back to Turkey under restraints. There were angry Kurdish protests in cities across the world.

Ocalan: Facing military justice

But many in Turkey hold him personally responsible for causing thousands of deaths during the 15-year armed struggle by the Kurdistan Workers' Party, or PKK.

There have been many demonstrations calling for his execution, especially by families who have lost relatives in the violence.

Lawyers' complaints

Mr Ocalan's lawyers have complained that they have been denied proper access to their client, and that they themselves have been beaten by police.

Ahmet Zeki Okcuoglu: Off the case

One prominent lawyer, Ahmet Zeki Okcuoglu, has withdrawn from the defence team.

He says his client will not get a fair trial, and that he does not want Mr Ocalan's death on his conscience.

Mr Ocalan's lawyers are contesting a comprehensive 139-page indictment.

They say they will argue that, if their client is executed, the war between the Turkish government and the PKK, which has already claimed 37,000 lives, will only escalate.

Questions over military justice

The trial has prompted debate in Turkey over military trials. The Prime Minister, Bulent Ecevit, has said he wants to do away with the military presence in the judicial process.

Security is intense around Imrali island

He and other leading politicians have acknowledged that the country is open to international criticism unless the court is restructured.

The European Court for Human Rights has repeatedly stressed that civilians should not be tried by a serving military officer because it undermines the independence of the court process.