Foreign Ministry spokesman Hong Lei said there had been no "enforced disappearances" at the Kirti monastery, in Sichuan province.
He said local authorities had taken some monks for "legal education".
Rights groups say the monastery has been locked down since a monk set himself on fire in March.
The security forces were involved in a stand-off with the monks for several week after the incident.
Witnesses and campaigners later said hundreds of monks had been detained illegally.
On Wednesday, UN officials asked China for details of the whereabouts of the monks.
"We encourage the authorities to undertake full investigations into the ongoing practice of enforced disappearances," said a statement from the UN's working group on enforced disappearances.
But in his weekly news conference, Mr Hong told journalists that no such thing was happening in the monastery.
"The relevant local authorities are conducting legal education for the Kirti monastery monks in order to maintain religious order there. There was no question of forced disappearances," he said.
Mr Hong added that "relevant organisations" should "abandon bias and be objective and fair".
Rights groups say paramilitary police raided the monastery in Aba, in the Sichuan province, in late April and detained more than 300 monks.
Analysts say tension has been high in Aba since Tibetan communities across western China rose up in protests three years ago.
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