A German judge has resigned from his role working in an UN-backed war crimes tribunal in Cambodia, citing interference from the Government of Cambodia.

The judge, Siegfried Blunk, described "repeated statements which will be perceived as attempted interference by government officials".

Whilst stating that he would not by swayed by such opposition, he said his "ability to withstand such pressure by government officials and to perform his duties independently could always be called in doubt."

Pressure has been placed on the tribunal to halt proceedings by current Cambodian Prime Minister and former Khmer Rouge commander Hun Sen, who left the movement before its collapse. He allegedly said further trials, beyond what was currently taking place “was not allowed”.

Blunk also quoted the Cambodian information minister, who he claimed said that judges who wanted to pursue further cases should “pack their bags and leave.”

The move comes a week after criticism from Human Rights Watch for failing "to conduct genuine, impartial and effective investigations" into what are known as Case 003 and 004.

The group went on to call for the resignation of both Blunk and his Cambodian counterpart.

Brad Adams, the Asia director at Human Rights Watch said,

“The investigating judges concluded their investigation into Case 003 without notifying the suspects, interviewing key witnesses or conducting crime site investigations.

This would be shocking for an ordinary crime, but it’s unbelievable when it involves some of the 20th century’s worst atrocities.”

Reports also emerged of criticism from within the UN, as members of staff wrote a private letter to Secretary General Ban Ki-Moon complaining of the way the crimes were being investigated, with one calling the tribunal “dysfunctional”.

UN deputy spokesman Eduardo Del Buey thanked Blunk for his service and said,

“The United Nations has constantly emphasized that the ECCC (Extraordinary Chambers in the Courts of Cambodia) must be permitted to proceed with its work without interference from any entity, including the ... government of Cambodia, donor states or civil society.”

An estimated 1.8 million people were killed during the Khmer Rouge’s rule in Cambodia in the 1970s. The court has so far spent about $100 million and handed down just one sentence.

The charges the defendants face include crimes against humanity, war crimes, genocide, religious persecution, homicide and torture.

See our earlier post: 'Khmer Rouge leaders deny charges as donors push for swift trial' (sep 2011)