The United Nations says the world body's top legal affairs official will visit Cambodia this week to discuss allegations of political interference from Phnom Penh in the ongoing Khmer Rouge trials.

Tribunal spokesman Lars Olsen, speaking Monday in the Cambodian capital, said Under Secretary-General for Legal Affairs Patricia O'Brien will meet Thursday and Friday with senior court officials and senior members of the Cambodian government.

The visit comes less than two weeks after one of two lead judges quit the tribunal after complaining of government interference. Siegfried Blunk said his resignation was triggered by ongoing government opposition to two new cases probing Khmer Rouge atrocities during the extremist communist group's 1975-1979 reign. Blunk said the government criticism made his continued role with the tribunal untenable.

The resignation also spawned calls from international human rights groups for stronger U.N. action to prevent government interference with the tribunal.

The world body has repeatedly accused senior government officials, including Prime Minister Hun Sen — himself a former Khmer Rouge cadre — of pressuring the tribunal not to pursue any more cases beyond the four already targeted. The prime minister has cited what he calls the threat of civil war if more cases are opened.

Meanwhile, critics of Blunk and fellow Judge You Bunleng have accused the jurists of politicizing the tribunal and urged both of them to step down. Human Rights Watch said early this month both judges had violated their judicial responsibilities and have no place on the court.

The tribunal was set up in 2006 to bring a measure of justice and closure to a nation still traumatized by the deaths of up to 2 million people while under Khmer Rouge rule more than three decades ago.

In its landmark first and only trial, the tribunal last year sentenced former Khmer Rouge lieutenant Kaing Guek Eav, better known as Duch, to 30 years in prison for his role as chief of the notorious Tuol Sleng torture prison.

The tribunal later reduced the sentence to 19 years, granting Duch credit for time served. Duch has appealed the guilty verdict, and the tribunal has said it hopes to rule by the end of this year whether the conviction should be overturned.

The trial of the four most senior surviving members of the former Khmer Rouge, including 79-year-old nominal head of state Khieu Samphan, opened earlier this year, but has since slowed as the court considers health issues related to the elderly defendants. They face charges of religious persecution, torture and genocide.

Khmer Rouge leader Pol Pot died in 1998.