He said the released protesters included 413 Buddhist monks, but added that 432 suspects, including 170 monks, were still in custody, while the investigation is ongoing.
Unrest began on March 10 when Buddhist monks in Lhasa, the capital of Tibet, held a demonstration marking the 49th anniversary of a failed uprising against Chinese rule.
Exiled Tibetans say Chinese forces cracked down brutally on demonstrators, killing around 140 people. Beijing says only 18 people were killed, many of them Han Chinese murdered by Tibetan separatists. Riots spread from Tibet itself to surrounding provinces, including Gansu.
As the disturbances continued, law enforcement authorities announced that they would offer "leniency to those who surrendered themselves."
The head of the Gannan Tibetan autonomous prefecture, Mao Shengwu, said on Wednesday that 2,204 people involved in the unrest had turned themselves in, but that the majority of these had later been released.
The world's most populous country has accused Tibet's spiritual leader, the Dalai Lama, of being behind the violence. Communist Party Secretary Zhang Qingli branded him "a wolf in monk's robes, a devil with a human face, but the heart of a beast."
The Dalai Lama has denied that he organized the riots.
Last month, the president of the European Parliament spoke of the possibility of a boycott by European leaders of the Olympic opening ceremony over China's heavy-handed response to the protests. The Olympic torch has been met by demonstrations in London, Paris and San Francisco.
