Chinese police opened fire on a group of protesters in Tibet, injuring 60, overseas rights organizations said today, in the latest flare-up over the authorities' tight control of the region.

The demonstrators had gathered on Sunday to demand the release of a fellow Tibetan detained for refusing to fly the Chinese flag, said the UK-based group Free Tibet.

"Security forces started beating the Tibetans, causing severe injuries, deployed tear gas and fired indiscriminately into the crowd," it said.

The shooting in Biru county left two protestors in critical condition, it added.

A policeman at Biru county public security bureau denied any incident to AFP, saying: "No protest, no one injured."