The United Nations has rejected media reports that it instructed judges at Cambodia's war crimes court to dismiss one of its cases linked to Khmer Rouge atrocities of three decades ago.

A spokesman for the U.N. secretary-general said Tuesday the court is an independent body and that the United Nations supports the independence of the judiciary in Cambodia and elsewhere.

Earlier this week, media reports said at least five U.N. employees in the court's investigations office left their posts in April after disagreements over the decision to close the tribunal's third case, which involves two former senior members of the Khmer Rouge military, suspected of a role in the deaths of thousands of people. The Cambodian government has opposed having the case go to trial.

International observers of the private Open Society Justice Initiative called on the U.N. Tuesday to investigate the conduct of two investigative judges, one German and one Cambodian, who decided to close the case.

The U.N. statement did not refer directly to the Initiative's request, but said the judges of the special war crime court in Cambodia must be allowed to function free from any external interference, whether they come from the U.N., Cambodia's royal government, donor countries or civil society.

The U.N. says as many as two million people died during Cambodia's communist regime between 1975 and 1979. The court has convicted one senior Khmer Rouge member so far, the head of a notorious prison camp where some 14,000 people died.

Critics have said that the court works too slowly and that some of the most senior Khmer Rouge leaders have died in the past 30 years.

Under an agreement signed between the U.N. and Cambodia, the war crimes tribunal was set up as an independent court, employing both Cambodian and foreign judges and other personnel.

The Open Society Initiative is funded by U.S. billionaire George Soros that has monitored the Khmer Rouge tribunal since 2003, three years before the court formally opened its doors.