A British lawyer charged with prosecuting Khmer Rouge war crimes has formally accused the international tribunal's investigating judges of exceeding their authority in a deepening spat.

Prosecutor Andrew Cayley has formally appealed an order from the German and Cambodian investigating judges that he retract recent remarks calling for a more complete investigation of two Khmer Rouge suspects.

Cayley argued in his appeal against the order that it was arbitrary and that it interfered with his obligation to inform the public of the court's workings.

The international tribunal has already convicted a notorious Khmer Rouge prison warden and will soon open the trial of the movement's top four surviving leaders. However tribunal officials are divided on whether to proceed with a third and fourth case in the face of stiff opposition from the government of Prime Minister Hun Sen.

The investigating judges, Siegfried Blunk and You Bunleang, announced in April that they had concluded their 20-month probe in Case 003. But Cayley objected, calling publicly for further investigation, including an examination of suspected mass graves and interrogation of the two suspects, whose names have not been disclosed.

The investigating judges, in turn, accused Cayley of disclosing confidential information and demanded that he retract the offending portions of his statement within three days.

The tribunal, involving Cambodian and international officials, was established with United Nations backing to prosecute suspected Khmer Rouge war crimes and crimes against humanity. More than 1.7 million people are believed to have been executed or died from starvation and overwork during the group's harsh rule in the late 1970s.