We cannot leave the issue half-way

Prime Minister Hun Sen

The UN announced on Friday it was withdrawing support for a joint tribunal because the court's impartiality could not be guaranteed.

The decision came ahead of Tuesday's UN war crimes tribunal in The Hague to try former Yugoslav leader Slobodan Milosevic for genocide and crimes against humanity during the 1990s.

Foreign diplomats and Cambodians have expressed shock at the UN's decision to pull out of the Cambodia tribunal. The UN has been pressing Cambodia to bring former Khmer Rouge leaders to trial for atrocities carried out during their rule between 1975 and 1979.

Some Cambodians fear a trial will divide the country

During the "killing fields" regime, 1.7 million people died through execution, torture, starvation and hard labour.

A key sticking point in the negotiations appears to have been the Cambodian Government's insistence that national law would take precedence over the agreement with the UN in the trials.

There was also disagreement on who should go on trial - Cambodia wants to restrict prosecution to about 10 selected Khmer Rouge figures.

Leaders detained

Hun Sen has said Cambodia is determined to press ahead with plans for a tribunal. He told reporters he might ask individual nations for help if the UN refused to change its mind.

Hun Sen was a junior Khmer Rouge commander

"We cannot leave the issue half-way," he said. "The law must be implemented."

The United States, Australia and the UK are among the countries urging the UN to resume negotiations with Cambodia.

Hun Sen also revealed plans to extend the detentions of the only two Khmer Rouge figures in detention until a tribunal can be set up.

Under the current detention period, former army chief Ta Mok, also known as "The Butcher", can be held without trial until March, and Kang Kek Lue - the head of the S-21 torture and execution centre - can be held until May.

The two have been held for nearly three years.

Hun Sen is one of several government ministers with a Khmer Rouge background, though he has not been implicated in any humanitarian crimes.