Investigating judges at the tribunal prosecuting Khmer Rouge war crimes have rejected a request to extend their probe into a third case that is opposed by the Cambodian government.

Judges Siegfried Blunk and You Bunleng ruled Tuesday that the request from international prosecutor Andrew Cayley was “invalid” because he had not secured the approval of his Cambodian co-prosecutor, who opposes pursuing the case. Cayley told VOA's Khmer service he will appeal the decision.

Cayley had protested after the prosecuting judges closed their 20-month investigation of so-called Case 003 in April, saying they had failed to visit suspected crime sites or even interview the two suspects.

The action exposed a deep rift in the United Nations-backed court, which has convicted one Khmer Rouge prison warden and is expected to try the top four surviving Khmer Rouge leaders later this year.

The tribunal has been collecting evidence for a third and fourth cases, but Prime Minister Hun Sen opposes any further prosecutions, saying they would divide the country.

The dispute between Cayley and the investigating judges broke into the open when the British prosecutor issued a public statement citing deficiencies in the initial investigation. The judges responded by ordering Cayley to retract his statement, saying he had disclosed confidential information. That order is under appeal.

Legal experts following the proceedings fear that Cambodian members of the tribunal have been influenced by pressure from the government. Cayley's Cambodian co-prosecutor has said she believes the suspects in Case 003 are outside the jurisdiction of the court.

The Khmer Rouge is blamed for the deaths of as many as 2 million people through executions, starvation and overwork during its period of harsh rule in the late 1970s.