The United Nations and Cambodia have agreed to set up an international genocide court to bring former leaders of the Khmer Rouge to justice.
UN negotiator Hans Corell arrived in Phnom Penh last week
An estimated 1.7 million people died at the hands of the brutal Maoist regime in the 1970s but despite evidence of their atrocities, no Khmer Rouge leader has ever been charged.
Negotiations on the proposed genocide court have been taking place for more than five years.
"We have agreed on a draft co-operation agreement in which the United Nations will assist Cambodia in the proceedings of a special tribunal," Cambodian negotiator Om Yentieng told reporters.
The news was warmly welcomed by the international community.
"This is a great step forward. It's real progress, it's what
we've hoped for," said British Ambassador Stephen Bridges.
The draft of the legal agreement now has to be approved by the UN and the Cambodian parliament.
The UN General Assembly overwhelmingly backed a resumption of talks on the tribunal after its legal team pulled out in February 2002 over a row about which side would control the proceedings.
UN Secretary General Kofi Annan said at the time that Cambodia could not guarantee the tribunal's independence, impartiality and objectivity.
An estimated 1.7m people died as a result of the Khmer Rouge regime
It is thought this time around the international community will give the court its approval.
Backing from the Cambodians is also likely as the chief negotiator is one of Prime Minister Hun Sen's senior ministers.
The Khmer Rouge ruled the country from 1975 to 1979.
Many victims died of starvation and torture during the regime.
Khmer Rouge leader Pol Pot died in 1998, but many of the regime's other senior figures are still living as free men.
The agreement on the tribunal has been widely welcomed.
"This is what I have been waiting for years and years," a torture camp survivor told Reuters news agency.
The Chaktomuk Theatre in Cambodia's capital Phnom Penh will probably be used as the venue for the trial.