Phnom Penh (dpa) - A German judge who jointly heads the investigation office at the UN-backed war crimes tribunal in Cambodia has threatened to file contempt-of-court charges against the tribunal's international prosecutor.

   The unprecedented development that two senior UN staff might face off within the tribunal's system came days after the prosecutor, Andrew Cayley, said an investigation by Judge Siegfried Blunk's office was deficient.

   Blunk did not reply Friday to emailed questions, but the Cambodia Daily quoted him as saying it could 'write any story you like' after he declined to say what lay behind the contempt-of-court charges.

   Cayley said Monday that he had reviewed the file prepared by Blunk's team on the third case in the prosecution of leaders of Cambodia's former Khmer Rouge regime and would request the investigating judges do more work on it.

   His comments seemed to confirm long-standing rumours that the judges have done little on the case.

   Cayley, a British national, told the German Press Agency dpa Tuesday that case three still needed 'a substantial amount' of investigation and called on Blunk's office to notify the suspects they were under investigation and to interview them.

   'And [there are] a number of other steps, including investigation of crime sites also originally named by the prosecution in the introductory submission, which haven't been investigated at all,' Cayley said.

   Tribunal observers have long feared the investigating judges are trying to shelve the tribunal's third and fourth cases. That would suit the Cambodian government, which has repeatedly said it would not permit those cases to go to trial.

  Asked whether the court was indeed trying to bury cases three and four, Blunk responded with a threat.

   'The use of the word 'bury' is insolent, for which you are given leave to apologize within two days,' Blunk wrote in an email Tuesday without specifying a penalty.

   Blunk's actions come at a critical time for the court as it prepares for its second case against four senior surviving Khmer Rouge leaders this year.

   Cases three and four involve five unnamed former Khmer Rouge, who between them are thought to be directly responsible for tens of thousands of deaths.

   But the investigating judges have refused to make public any details about either case, including which crime sites were under investigation, leading to accusations that they have deliberately excluded victims.

   Tribunal monitor Clair Duffy of the Open Society Justice Initiative, which is funded by US billionaire George Soros and monitors the tribunal, said Friday that the case-three investigation had already done substantial damage to the tribunal's reputation.

   She said news of possible contempt-of-court proceedings was 'potentially very damaging.'

   'The potential message is that those seeking to act independently of political will and to act with integrity in the pursuit of justice will be laying themselves open to criminal sanction,' Duffy said.

   In its first case, the tribunal last year convicted the Khmer Rouge's head of security, Comrade Duch, of war crimes and crimes against humanity.

   More than 2 million people are thought to have died under the movement's rule of Cambodia from 1975 to 1979.

END