China has arrested 139 people in Xinjiang for allegedly spreading jihad, state-run media said Wednesday, as it warns of growing religious extremism in the far western region, home to Muslim Uighurs.

Another 256 people had been "punished" for spreading online rumours, the Global Times said citing local authorities, without specifying the measures taken.

Beijing has pointed to violent incidents to indicate a rising militant threat among the ethnic minority, but information in the vast region is tightly controlled and Uighur organisations complain of cultural and religious repression.

Police in Xinjiang have "handled an increasing number of cases in which individuals have posted or searched for religious extremist content on the Internet", the China Daily said, citing an unnamed source in the Xinjiang Daily.

In the two months to the end of August, 139 people were arrested for "spreading religious extremism including jihad", it said.

Also citing the Xinjiang Daily, the Global Times said a farmer in Hotan was detained after he uploaded 2GB of e-books about secessionism which were read 30,000 times.

"Overseas hostile forces have never stopped infiltrating and inciting residents to take up extreme religious ideas through the Internet and the online spreading has become a great threat to ethnic unity and social stability," the Global Times said, citing police.

Dilshat Rexit, a spokesman for the overseas-based World Uyghur Congress, which Beijing calls a separatist group, said the claims were a "total distortion of the truth" aimed at blocking Uighurs from going online.

Those detained had "expressed discontent with Chinese rule and systematic repression in the area", he said.

China's goal "is to suppress Uighurs' use of the Internet to obtain information and express different points of view", he added.

News of the detentions comes just ahead of the start of the Muslim Hajj, when almost 12,000 Chinese pilgrims are expected in Mecca according to reports.

China's state-run media have previously reported that Uighurs have fought in Syria's civil war against the regime, then returned home to put their militant experience into practice.

Members of a gang behind what China called a "terrorist attack" in Lukqun in June that left 35 people dead watched extremist videos beforehand, the China Daily said, citing police.

A court sentenced three people to death and one person to 25 years in jail in September over the attack, saying they had taken part in a "terrorist organisation", the official news agency Xinhua reported at the time.

The clash was Xinjiang's deadliest since 2009, when riots between Uighurs and China's ethnic majority Han left 200 people dead.

Xinjiang's population is 46 percent Uighur and 39 percent Han, according to official statistics, but the latter largely dominate the economy and form a majority in the regional capital Urumqi.