Judge Laurent Kasper-Ansermet submitted his resignation, effective in May, from the Extraordinary Chambers in the Courts of Cambodia, the United Nations said Monday.
He has served as international co-investigating judge since November, when his predecessor, Siegfried Blunk, resigned due to the Cambodian government's alleged interference in the court's proceedings.
U.N. spokesman Eduardo del Buey said the situation at the tribunal is of "serious concern."
Kasper-Ansermet, in a release on the tribunal's Web site, said his authority to investigate former senior members of the Khmer Rouge military -- Cases 003 and 004 -- has been constantly contested by You Bunleng, a national co-investigating judge.
Kasper-Ansermet said present circumstances "no longer allow him to properly and freely perform his duties."