Courts in a restive region of west China with a large Muslim population have jailed 20 people for up to 15 years for using the Internet to incite separatism and "holy war", state media said Thursday.

The sentences were immediately condemned by a group representing China's mostly Muslim Uighur ethnic minority, which said they were aimed at silencing critics of Beijing's policies in the Xinjiang region.

"These criminals used mobile phones, and other media to watch, copy and publicise 'holy war' and terrorism through pictures and audio visual materials," a report on the trials in on Xinjiang's government-run Tianshan news site said.

"They used moveable hard drives to urge crimes of separatism, religious extremism and terrorism, or used the Internet ... to download and transmit audio-visual materials and documents on religious extremism."

Xinjiang is home to around nine million Uighurs, a Turkic speaking minority people, many of whom accuse China's leaders of religious and political persecution.

The region has been rocked by repeated outbreaks of ethnic violence, but China denies claims of repression, saying it has brought economic growth and prosperity to the landlocked region bordering Central Asia.

The sentences come after Xinjiang's top leader vowed last month to strike with an "iron fist" against separatist forces in the region, as a heavy security presence was rolled out for the anniversary of deadly ethnic rioting in 2009.

According to the report, one of the five cases included eight people in Xinjiang's Aksu region who were jailed for up to 13 years for transmitting publications inciting separatism, religious extremism and terrorism.

Three others were sentenced in Kashgar city to up to 15 years for watching videos on "holy war" or "jihad" and circulating printed materials and books inciting holy war, it said.

The others were jailed for up to 13 years for similar crimes, including four people convicted in the regional capital Urumqi for "inciting terrorism" through the Internet.

"China is meting out heavy sentences to Uighurs who use the Internet to access information that is not controlled by the authorities and who are expressing opposing political views," Dilxat Raxit, spokesman for the World Uyghur Congress, told AFP in a statement.

"These people were seeking freedom and were fighting against institutional persecution."