The United Nations has warned Cambodia to stop negative comments about war crimes tribunal cases.

U.N.'s undersecretary-general for legal affairs, Patricia O'Brien said she had issued her warning during a meeting with government officials in Pnom Penh late Thursday.

The U. N. has been concerned about the tribunal's independence after an international investigating judge, German Siegfried Blunk, resigned earlier this month. Human rights groups have criticized Blunk for alleged failing to fully investigate new suspects for the court, which is seeking justice for an estimated 1.7 million people who died of starvation, exhaustion, lack of medical care or torture during the communist Khmer Rouge's 1970s rule.

He said that Prime Minister Hun Sen, Foreign Minister Hor Namhong and Information Minister Khieu Kanharith had all made statements demonstrating government opposition to the two cases he was investigating, creating an atmosphere in which he would be perceived as biased, no matter his judgment on the cases.

O'Brien “strongly urged the government to refrain from statements opposing the progress of the two cases and to refrain from interfering with the judicial process.

The U.N.-backed Khmer Rouge tribunal is gearing up for a major trial against the four surviving leaders of the Khmer Rouge, set to start in November.

Ahead of the trial, the court has to decide whether one of the defendants Leng Thirith, the former social affairs minister, is fit to stand trial. Medical experts say she has dementia, but the prosecutors and lawyers for civil parties do not agree.

The Khmer Rouge held power from 1975 to 1979. In the only case that has been heard so far, Kaing Guek Eav, known as Duch, who ran the main Khmer Rouge prison, was sentenced to 30 years last year, a term that was reduced to 19 years.