Caroline Gluck in Cambodia: "The foreign aid is vital"

Hun Sen told a donors conference in Tokyo that a trial would destroy the fragile fabric of his country and that revenge and retribution would return Cambodia to the dark ages.

There is growing pressure to see the perpetrators of Cambodia's notorious "killing fields" face justice for their crimes.

Two of the principal architects, Khmer Rouge leaders Khieu Samphan and Nuon Chea, switched to the government side in December after striking a deal with Prime Minister Hun Sen.

Several Western countries, including the United States and Britain, have said the pair should be put on trial for genocide.

Hun Sen's rival, Prince Norodom Ranariddh, president of the National Assembly, has said a trial cannot be avoided.

Aid promises

Hun Sen came to Tokyo in the hope of securing $1.3bn of aid for his country and he has reassured donors that aid would be properly used.

Juliet Hindell: "The aid would be used to get Cambodia back on its feet"

BBC Correspondent Juliet Hindell in Tokyo said the conference of 16 countries and international financial institutions seems predisposed to grant some aid, though there has been some discussion about securing improvements in human rights in return for funds.

Hun Sen: Plea for aid

Hun Sen promised the conference to uphold human rights, root out corruption and cut the size of the army and police force so that more money could be used for health and education.

He also criticised those opposed to aid for his regime as being anti- Cambodian.

Sam Rainsy, the Cambodian opposition leader, is also in Tokyo to observe the conference.

He is against giving aid to Cambodia and what he called the corrrupt regime.

The Wold Bank official who is chairing the conference, Ngozi Okinjo-Iwealla, said any commitment of funds would be based on the understanding that the Cambodian government would deliver actions, not words, and persevere with difficult reforms.