China - Chinese President Hu Jintao, forced to abandon a G8 summit in Italy by ethnic violence in restive Xinjiang, said that maintaining social stability in the energy-rich region was the most urgent task, state television reported on Thursday.

Hu described Sunday's riots in the regional capital Urumqi, where 156 people were killed and 1,080 wounded when minority Muslim Uighurs attacked majority Han Chinese, as a serious violent crime elaborately planned and organized by 'three forces' at home and abroad, an apparent reference to religious extremists, separatists and terrorists.

Hu, who doubles as Communist Party chief, told the decision-making Politburo late on Wednesday that local authorities should isolate and deal a blow to the small group of rioters and to unite and educate the majority of Uighurs.

Foreign Ministry spokesman Qin Gang shrugged off Turkey's call for the U.N. Security Council to discuss ways of ending the violence, saying Xinjiang was an internal affair.

Thousands of Chinese troops took up position in the riot-damaged streets of Urumqi in a show of force aimed at stifling ethnic violence.

State television showed Zhou Yongkang, China's top official in charge of security, and Public Security Minister Meng Jianzhu, reviewing camouflaged troops in Urumqi. Meng and Zhou were active in the crackdown on Tibetan areas after widespread demonstrations there last year.

Some residents worried about how the two sides could ever co-exist again.

Beijing cannot afford to lose its grip on Xinjiang, a vast desert territory that borders Russia, Mongolia, Kazakhstan, Kyrgyzstan, Tajikistan, Afghanistan, Pakistan and India, has abundant oil reserves and is China's largest natural gas-producing region.

This whole thing may go on for a few days, but eventually the government has to use force, there's no question about that, said Bo Zhiyue, senior research fellow and China politics expert at National University of Singapore's East Asian Institute.

Because if you don't use force, the whole thing will snowball. It would spin out of control. Any government would have to do something about it.

Han Chinese, who have said they feel threatened after Sunday's violence, cheered Thursday's show of military might as the trucks rolled into the city and took pictures. Uighur residents looked on with strained faces.

This makes me scared and I think it's meant to, said a Uighur woman called Adila. What can we do against so many soldiers?

Authorities have posted notices in Urumqi urging rioters to turn themselves in or face stern punishment. Li Zhi, Communist Party boss of Urumqi, said he would seek the death penalty for rioters who resorted to murder in a city divided between Uighurs and Han, the country's predominant ethnic group.

Those who gave themselves in would be treated more leniently or even avoid punishment, the notices said. Anyone who provided evidence or turned in suspects would be rewarded and protected by the police, they said, providing a hotline.

People must not use mobile phones or the Internet to create and spread rumors, to link up with others, incite trouble, or disturb the social order, one notice added. The Internet has been cut in many areas.

The mixture of threat and reward echoed Chinese notices after demonstrations in the Tibetan capital, Lhasa, turned violent in March last year in the run-up to the Beijing Olympics.

It was unclear whether mosques would open in Urumqi on Friday, the Muslim day of prayer. Allowing the mosques to open could provide a forum for discontent. Closing them could further stoke grievances.

People coming to worship must all go home to do it. Thank you for your cooperation, said a notice on the front door of the Qinghai mosque in Tianshan district.

Muslims gathered at the mosque said they would be disappointed, even angry, if they were not allowed to pray there.

We still don't know whether we'll be able to pray tomorrow, said Bai Ping, a Han convert to Islam. They are afraid of trouble inside the mosque.

Xinjiang has long been a tightly controlled hotbed of ethnic tension, fostered by an economic gap between Uighurs and Han, government curbs on religion and culture and an influx of Han migrants who are now the majority in Urumqi.

On Thursday, a line of troops, armoured vehicles and trucks measuring several kilometers and blasting out the propaganda passed for about 25 minutes through Saimachang, the Uighur neighborhood where hundreds of women protested on Tuesday.

Helicopters flying only a few meters above rooftops scattered propaganda leaflets, urging ethnic unity, over the crowd of hundreds who gathered to watch the security forces march by.

Troops mounted on the truck with guns and riot shields shouted slogans in unison and some of the trucks carried signs in Chinese, one of which read separatists bring calamity to the country and its people.

Financial markets have been unaffected by the violence.

(Additional reporting by Ben Blanchard in Shanghai and Yu Le, Lucy Hornby and Benjamin Kang Lim in Beijing, and Augustine Anthony in Islamabad; Editing by Nick Macfie and Jeremy Laurence)