PHNOM PENH, Cambodia - The Canadian prosecutor at the genocide tribunal trying Cambodia's Khmer Rouge announced Tuesday he is resigning, citing personal and family reasons.

Robert Petit said in a statement that his resignation will become effective September 1, three years after he joined the United Nations-backed tribunal, which is currently holding its first trial.

"It has been the greatest privilege of my career to have the opportunity to bring some justice to the victims of the crimes of the Khmer Rouge," Petit said.

"I remain convinced that Cambodias hopes for a better future lie, in part, on true accountability for crimes."

The Khmer Rouge are believed responsible for the deaths of 1.7 million people from forced labour, starvation, medical neglect and executions when they held power in 1975-78.

It was not clear how Petit's resignation will affect the tribunal's work. The statement said the process of finding his replacement had already begun.

The tribunal is currently trying Kaing Guek Eav, also known as Duch, who commanded the Communist group's S-21 prison in Phnom Penh.

He is charged with crimes against humanity, war crimes, murder and torture. Four other senior Khmer rouge leaders are in custody, awaiting trial.

Petit did not elaborate on his reasons for stepping down as co-prosecutor.

Lars Olsen, a tribunal spokesman said his resignation was purely for the sake of his family and had nothing to do with politics or disagreements with his Cambodian co-prosecutor.

The tribunal has been dogged by disagreements over procedure and political wrangling, which has led to many delays. Allegation of corruption among the tribunals Cambodian staff have also hurt its credibility.

Petit has found himself at odds not only with opponents in the defence, but also with his co-prosecutor Chea Leang. The court operates under a hybrid system in which international and Cambodian jurists work in tandem.

Petit has said that he would like to see as many as six more former Khmer Rouge charged, but Chea Leang has opposed the idea, saying it is contrary to the agreement between Cambodia and the UN establishing the tribunal, and could endanger peace in the country.

Cambodian Prime Minister Hun Sen said in March that expanding the scope of the tribunal could spark a war and cause the deaths of hundreds of thousands of people.

Critics charge that Hun Sen's government has sought to limit its scope because other suspects are now loyal to Hun Sen, and to arrest them could cause him political trouble.