SIX more potential candidates for prosecution have been identified by Cambodia's war crimes tribunal, sources close to the UN-backed court say.

The court's international co-prosecutor Robert Petit, who proposed the investigations, would not confirm the number or names of the potential suspects citing legal reasons, but said the possibility of more cases should come as no surprise.

"There's always been a higher number than five accused discussed during and after the negotiations," he said in an interview Monday. "Those new cases represent, as far as I'm concerned, the extent of which the prosecution will be," Petit added.

Sources close to the court say three more cases are expected - two new and one supplementary - involving six additional suspects.

Petit's Cambodian counterpart, Chea Leang, has refused to sign off on the second submission, prompting Petit to lodge a "statement of disagreement". The court's pretrial chamber must now resolve the impasse, which threatens to further delay the trials.  

Chea Leang repeatedly declined comment Tuesday, saying she was "too busy".  

The court's internal rules say she must respond to Petit's submission this week.  

Observers have urged the Cambodian side of the court to demonstrate its independence by allowing further investigations to begin.

"If ever there was a moment to show that the Court is not a tool of the Cambodian government, this is it," Open Society Justice Initiative's executive director, James Goldston, wrote  in an email.