The international prosecutor at Cambodia's Khmer Rouge war crimes tribunal announced his resignation from the court Tuesday.

Canadian prosecutor Robert Petit says that "for personal and family reasons" he would soon leave his position at the UN-backed court, which is formally known as the Extraordinary Chambers in the Courts of Cambodia (ECCC).

"I remain convinced that Cambodia's hopes for a better future lie, in part, on true accountability for crimes," Petit said in the statement.

"My staff and I have tried, within our jurisdiction, to contribute to that goal to the best of our abilities," he added.

The court's long-awaited first trial has seen Kaing Guek Eav, better known by the alias Duch, accept responsibility for overseeing the torture and execution of more than 15,000 people at Tuol Sleng prison.

Four other Khmer Rouge leaders are also in detention awaiting trial, but while Petit has sought to bring more cadres to justice, Cambodian co-prosecutor Chea Leang has refused to expand the list of the accused.

Petit has previously clashed with his Cambodian co-prosecutor over whether to go after more suspects from the hardliner communist movement at the tribunal.

Lawyers for detained former Khmer Rouge ideologue Nuon Chea have accused Petit of knowing that the Cambodian government ordered his co-prosecutor not to pursue more former regime members.

In a letter to Petit distributed to the press Tuesday, Nuon Chea's lawyers Michiel Pestman and Victor Koppe demanded a written reply to the allegation by the end of this week.

Petit was not available to comment on the allegations, and is due to formally leave his position in September.