The top Communist official in China's Xinjiang said Tuesday that extremists from the mainly Muslim region have been apprehended after returning from fighting in Syria with the Islamic State group.

Zhang Chunxian, party head in Xinjiang, told reporters that the radicals were caught when a terror plot was recently uncovered, reported the Global Times, which is affiliated with the ruling party mouthpiece People's Daily.

He said that they had returned to Xinjiang, the homeland of China's Uighur ethnic minority, to participate in violent terror plots, the report said. He apparently gave no details, including the number of people apprehended.

Other Chinese media carried similar reports, but did not specifically mention Syria.

Fighters for the IS jihadist group have taken control of a wide swathe of Iraq and Syria and drawn global revulsion by filming the beheadings and killings of captives, including foreign civilian aid workers and journalists.

Xinjiang, in far western China, has seen a wave of unrest, labelled by authorities as "terrorism" and blamed on "separatists", which has sometimes spread to other parts of the country.

Among the most shocking attacks was a deadly rampage by knife-wielding assailants at a train station at Kunming in China's southwest in March, when 31 people were killed and four attackers died.

More than 30 people were killed in an assault on a market in the Xinjiang regional capital Urumqi in May, prompting China to launch a crackdown, detaining hundreds of people described as suspected terrorists.

Beijing has consistently warned that radical forces from outside the country have inspired terror attacks in the resource-rich, mainly Muslim region bordering Central Asia, as well as outside it.

China regularly accuses what it says are exiled Uighur separatist groups such as the East Turkestan Islamic Movement and the Turkestan Islamic Party of being behind attacks.

But overseas experts doubt the strength of the groups and their links to global terrorism, with some saying China exaggerates the threat to justify tough security measures in Xinjiang.

Rights groups say that harsh police treatment of Uighurs and government campaigns against religious practices, such as the wearing of veils, has led to violence.

China defends its policies, arguing that it has boosted economic development in the area and that it upholds minority and religious rights in a country with 56 recognised ethnic groups.

Zhang said that 230 government employees were killed in the Xinjiang violence in 2013, the People's Daily reported, without specifying their ethnicities.

More than 450 people were killed in Xinjiang last year, a rights group said last week -- with three times as many deaths among members of the mainly Muslim Uighur minority than ethnic Han Chinese.

Information in the area is strictly controlled by authorities, and the Washington-based Uyghur Human Rights Project used data from Chinese and overseas media reports for its analysis, giving ranges for most of its figures.