Authorities in China's restive Xinjiang region have sentenced nine people to death for "violent terrorism" crimes, state media reported, as part of a nation-wide crackdown on alleged separatist groups.

The announcement comes as state news portal Xinjiang Net reported on Thursday that another 29 suspects had been rounded up on charges such as inciting separatism, in the regional capital Urumqi, the site of a suicide bombing that killed 39 people last month.

A total of 81 people from Xinjiang, home to a large Muslim Uighur minority, were handed sentences for crimes related to involvement in "terrorist organisations" to intentional homicide and arson, state broadcaster CCTV said on a microblog.

"Among those, nine people were sentenced to death, and three people were given death sentences with a two-year reprieve," CCTV said, the latter referring to a sentence that is often commuted to life in prison.

Others were given life in prison or shorter sentences.

China has launched a year-long "anti-terrorism" operation, and hundreds of suspects have already been detained.

Only last week, 55 people were also found guilty of "terror links" in Xinjiang's city of Yining, and the verdicts were delivered before a crowd of 7,000 at a sports stadium.

Economic marginalisation

Experts said economic marginalisation of Uighurs is one of the main causes of the violence, which has killed at least 180 people across China in the past year.

They argued that benefits of development in Xinjiang, a resource-rich and strategically located region on the borders of ex-Soviet central Asia, have largely gone to majority Han Chinese, stoking resentment among Uighurs.

Rights groups have also expressed concerns about whether terror suspects in the region are granted fair trials, given the common use of forced confessions in the Chinese legal system.

"Lack of justice and legal procedure will lead to more people losing their freedom for political reasons," Dilshat Rexit, a spokesman for the exiled World Uyghur Congress, said in a statement.

Information about Xinjiang is difficult to verify independently, with foreign and local journalists subject to heavy restrictions.

Beijing said separatist groups in Xinjiang are seeking to form their own state called East Turkestan, though experts dispute the influence and reach of the most prominent group, the East Turkestan Islamic Movement (ETIM).