SHANGHAI  China said Wednesday that 660 people implicated in Tibetan protests and riots in western China over the past two weeks had surrendered to the authorities.

The announcement was part of the government’s effort to quell continuing unrest in the area, which includes Tibet and adjoining provinces with large Tibetan populations. It is the worst outbreak of anti-Chinese violence in 20 years.

It was unclear from the announcement how many of the 660 had surrendered voluntarily and how many would be formally charged with criminal offenses. Nor was it clear whether all were ethnic Tibetans.

The unrest, which began with a March 14 riot in Lhasa, the capital of Tibet, has already cast a pall over preparations for the Olympic Games in Beijing this summer and energized human rights advocates and others who contend that China’s rule over the area has been harsh and that Tibet should be independent.