Cambodia is encouraging former Khmer Rouge soldiers to disarm

The agreement was signed in Phnom Penh by UN legal counsel Hans Corell and his Cambodian counterpart, Sok An.

I cannot forget the time I was tortured. Every day, I'm wanting this trial Chum Manh Khmer Rouge's legacy of fear

Mr Corell warned on Thursday that it was still "far too early" to say when the trials would actually begin.

The agreement must still be ratified by Cambodia's legislature, and that is not expected to happen before the country holds a general election on 27 July.

BBC correspondent Clare Arthurs says the UN will also need to ensure that those nations which have been pushing for the hearings, including the United States, quickly commit the necessary funds in order for the tribunals to start.

The Cambodian Government and the UN first began negotiations to set up an international tribunal in 1997.

But for years, the two sides struggled to agree on the level of foreign control over the proceedings.

The UN pulled out of the talks in early 2002, saying Phnom Penh was unable to guarantee conditions for a fair trial.

Talks resumed last year, and the current proposal was suggested.

The plan - agreed in draft form in March - allows the majority of the judges to be Cambodian, but requires at least one foreign judge to support a tribunal ruling.

Human rights groups have criticised the agreement as giving the Cambodian Government too much say in the proceedings.

But others have argued that time is running out to bring Khmer Rouge leaders to justice.

Nearly 2 million Cambodians are thought to have died under Khmer Rouge rule between 1975 to 1979.

So far, no senior figures have been charged for the genocide - one of the 20th Century's worst atrocities.

Most senior Khmer Rouge figures are now elderly, and some - including the top leader, Pol Pot - have already died.