(Tibetan monks walk at Drepung Monastery in Lhasa, Tibet Autonomous Region, July 19, 2009/Grace Liang )

China on Thursday defended its treatment of Tibetan monks it says are undergoing re-education, responding to a U.N. inquiry about what exiled Tibetans have called the forced disappearance of hundreds of monks.

Foreign Ministry spokesman Hong Lei said the monks had not been detained illegally, and urged U.N. human rights investigators to act without prejudice. “It is legal to supervise religious affairs, and protect normal religious order. This issue of forced disappearance fundamentally does not exist,” Hong told reporters at a regular press briefing.

U.N. human rights investigators called on China to reveal the “fate and whereabouts” of more than 300 monks who disappeared after being rounded up by security forces at a monastery in Aba prefecture of the southwestern province of Sichuan in April.

Exiled Tibetans and a prominent writer have said that the crackdown was sparked by a monk’s self-immolation in March, an apparent protest against government controls.