Police shot dead 12 mobsters during the July 5 riot in Urumqi, a senior official has said - the first time the government revealed the extent of force used by security forces in the worst violence in that region in decades.

On the night of the riot, police in Urumqi "resolutely" shot the mobsters after firing guns into the air had no effect on these "extremely vicious" thugs, Nur Bekri, chairman of the Xinjiang Uygur regional government, said in an interview over the weekend.

Bekri said three of them died on the spot while nine died later. He did not reveal which ethnic group the mobsters belonged to.

"The police showed as much restraint as possible during the unrest," Bekri said, adding that many officers were injured and one was killed after being hit by mobsters.

Families of the victims could receive a compensation of 200,000 yuan ($29,270) from the government and possibly another 200,000 yuan from an ethnic unity foundation set up after the riot with donations from the public, Bekri said.

Bekri said authorities had received information about the protest beforehand but had not expected such violence to erupt.

"We could never imagine that the mobsters were so extremely vicious and inhumane," he said, adding that the government believed the rioters had prepared weapons in advance for use in coordinated attacks.

"We really didn't expect that," he said.

Xinhua News Agency cited police authorities as saying it received reports that rioters had attacked people and property in more than 50 locations across the city on July 5.

It said the rioters, most of them from other parts of the region, appeared to have been well organized, saying weapons were gathered in advance.

In the days preceding the riots, there were "noticeably hot" sales of long knives, some of which were used in the attacks, the report quoted vendors as saying.

The presence of alleged ringleaders, including several women in long, black Islamic garb and black head scarves who issued "commands" to rioters, was also noted in the report.

"Such dressing of women is very rare in Urumqi, but these kind of women were seen many times at different locations on surveillance cameras on that day," the report quoted unnamed local police authorities as saying.

Bekri said that as the situation is becoming more stable, "it won't be long" before the Internet was completely reopened to the public.

He said that during the riot, the Internet and cell phone messages became the main communication methods for mobsters, and it was necessary for the government to shut down the Internet to stabilize the situation and restore social order.

Experts have warned that terrorism might be the real driving force behind the Urumqi riot.

The World Uygur Congress, which China alleges instigated the riot, is closely associated with the East Turkestan Islamic Movement (ETIM), a group labeled by the UN and the US as a terrorist organization, said Rohan Gunaratna, who heads the International Center for Political Violence and Terrorism Research at Nanyang Technological University in Singapore.

"The ETIM is a big threat for the central Asian area. China needs more anti-terror specialists and should improve intelligence work on the ETIM and train more police in counterterrorism," he said.

Some Chinese legal experts also suggested after the Xinjiang riot that the government have more effective anti-terror legislation.

"The nature of the riot has the major characteristics of a typical terrorist attack," said Bo Xiao, director of the Commission for Legislative Affairs of the Standing Committee of Xinjiang regional People's Congress.

China should establish a special law for counterterrorism in addition to the current less explicit regulations scattered throughout different laws, he said.