Chinese police shot at Tibetan prisoners to quell a pro-independence demonstration inside Tibet's most notorious prison, a Tibetan rights group said Saturday.

The India-based Tibetan Center for Human Rights and Democracy said it was not known how many prisoners were killed or injured by the police in stopping the May 1 protest.An official in the Tibetan government office handling media inquiries denied any protest or police suppression occurred.

The Tibetan rights group said news of the demonstration came in a letter sent from Tibet and gave the following account:

About 150 prisoners unfurled the banned Tibetan national flag and demonstrated inside Drapchi prison, on the outskirts of the Tibetan capital of Lhasa. Local police and the paramilitary People's Armed Police were called in and fired on the protesters. Many protesters were believed to have been placed in solitary confinement and then tortured.