Image copyright AFP Image caption Mr Kasper-Ansermet said he had been blocked in efforts to investigate two further suspected cases.

A second judge has resigned from the troubled UN-backed international war crimes tribunal in Cambodia.

Swiss Judge Laurent Kasper-Ansermet said he was leaving because his Cambodian counterpart, You Bunleng, had thwarted attempts to investigate former members of the 1970s regime.

Mr Kasper-Ansermet said the dispute had left him unable to work properly.

In October last year, another judge, German Siegfried Blunk, resigned for similar reasons.

The row relates to attempts to bring two potential new cases - known as cases 003 and 004 - to the tribunal.

In a statement released by the tribunal, Mr Kasper-Ansermet said: "You Bunleng's active opposition to investigations into cases 003 and 004 has led to a dysfunctional situation."

He added that he "considers that the present circumstances no longer allow him to properly and freely perform his duties".

'Interference'

At the time of his resignation, Mr Blunk, who was replaced by Mr Kasper-Ansermet, accused the Cambodian authorities of political interference in the two cases.

Critics accuse the government of being reluctant to have further figures of Khmer Rouge regime investigated.

The court was jointly created by the UN and the Cambodian government, and includes both Cambodian and international judges.

It successfully concluded its first case in February, sentencing the chief jailer of the Khmer Rouge, Comrade Duch, to life imprisonment for his role in running a notorious prison where thousands of inmates were killed.

The tribunal is currently hearing the case of the three most senior surviving Khmer Rouge leaders, who are accused of taking part in mass killings in the 1970s.

Testifying against the three men on Monday, Comrade Duch, born as Kaing Guek Eav, told the court that he had been instructed to torture inmates by putting plastic bags over their heads and watching them suffocate.

Asked who had told him to do so, he said it had been ordered by his supervisors and that it was party policy and sanctioned by official documents.

The three accused - Nuon Chea, Khieu Samphan and Ieng Sary - have pleaded not guilty to charges that include crimes against humanity, genocide and torture

Up to two million Cambodians are thought to have died - from starvation, overwork or execution - during the four years of Khmer Rouge rule.