As many as two million people died during the Khmer Rouge's control of the country, between 1975 and 1979.

But the period was removed from the school history curriculum after the 1991 Paris peace accords began a process of reconciliation between Cambodia's warring factions, including the Khmer Rouge.

The Khmer Rouge ultimately pulled out of the peace process in 1992 and continued a campaign of guerilla warfare.

The UN representative on human rights in Cambodia, Thomas Hammarberg, raised the issue with the country's Education Minister, Tol Lah.

"The next generation of Cambodians do have the right to know about this," he said.

Political barriers

The minister said that at the time of the peace accords, ending Cambodia's protracted civil war was of paramount importance to the government.

But with attention now focused on bringing the leaders of the seriously weakened Khmer Rouge to justice, it was time to end the educational blackout.

"I'm in favour of teaching the history," said Tol Lah. "It must be told again and again so history does not repeat itself."

But changing the policy could take time, he warned, as politics will continue to play a major role in how Prime Minister Hun Sen's coalition government decides to proceed.

The recent surrender of several fugitive Khmer Rouge leaders and the arrest of rebel army chief Ta Mok has speeded up efforts to provide justice to the victims and survivors of the "killing fields".

The UN Secretary-General, Kofi Annan, has called for the creation of an international tribunal to try Khmer Rouge leaders for crimes against humanity, but Hun Sen says they should be tried in the Cambodian courts.

Mr Hammarberg is due to meet Hun Sen on Thursday to discuss the possibility of international assistance for a Cambodian trial.