BEIJING - At least 81 people in Tibet have been detained for suspected criminal activity amid a security sweep in the Himalayan region, including two who are being held for having "reactionary music" on their mobile phones, state media reported.

Tibet independence advocates said Wednesday the anti-crime crackdown appeared to be aimed at intimidating Tibetans ahead of sensitive anniversaries in coming weeks, including the 50th anniversary of a crushed independence uprising.

China has been preparing for the possibility of more unrest in Tibet since deadly rioting in the capital Lhasa on March 14 last year sparked the biggest anti-government protests among Tibetans in decades -- and a major military crackdown.

The public security bureau of Lhasa, the region's capital, launched a "strike hard" campaign against crime on Jan. 18, with raids on numerous residential areas, rented rooms, hotels, guesthouses, Internet cafes and bars, the Tibetan Daily said in a report on the China Tibet News.

By Saturday, authorities had detained 51 people for unspecified criminal activities and taken in another 30 people for robbery, prostitution, theft, according to the report dated Sunday.

Two people were being held because "reactionary music" was found in their cell phones, the report said.

A woman who answered the phone at the Lhasa public security bureau hung up after saying the office was not authorized to speak with the media. Calls to the Lhasa government office rang unanswered Wednesday amid a weeklong national holiday to celebrate the Lunar New Year.

The International Campaign for Tibet said the latest "strike hard" campaign "appears to be intended to intimidate Tibetans still further" ahead of the Tibetan New Year in late February and the period in March that marks the 1959 independence uprising and the Dalai Lama's flight to India.

The 'strike hard' campaigns are crime crackdowns in which normal arrest and prosecution procedures are usually waived to maximize the numbers detained. Though they normally focus on criminals, in places like Tibet and the restive northwest region of Xinjiang, people suspected of anti-government activities are also targeted.

In December, Chinese state media reported that authorities in Tibet detained 59 people accused of disseminating rumors aimed at inciting ethnic tension and were cracking down on illegal downloads of "reactionary music" online.