Troops patrol riot-hit Urumqi

Chinese officials have launched a sweeping crackdown in an effort to keep a lid on ethnic clashes [EPA] urumqi Voice-Thousands of Chinese troops are patrolling the streets of Urumqi, capital of the far western Xinjiang region, in an effort to maintain the peace between the city's ethnic Uighurs and Han Chinese. Clashes between the groups have paralysed the city since Sunday when a street protest by Uighur demonstrators turned into some of the bloodiest ethnic violence seen in China in years. Chinese officials say the violence has left more than 150 people dead and around a thousand injured. Reporting from Urumqi on Thursday, Al Jazeera's Melissa Chan said that while a strong military presence remained, the city appeared to be returning to some kind of normality. Twitter Follow Al Jazeera's China reporter Melissa Chan. Live Twitter feed What is twitter? However, she said tensions remained high athough there had been no reports of further clashes as had occured on previous days. Long convoys of armoured cars and troop trucks have been patrolling the streets of Urumqi, with a particularly heavy presence in Uighur neighbourhoods of the predominantly Han Chinese city. Army helicopters have also been conducting regular flights over the city. The patrols and an overnight curfew are part of a sweeping crackdown ordered by the Chinese authorities in an effort to keep a lid on the unrest. 'Execute them' In depth Q&A: China's restive Uighurs Xinjiang: China's 'other Tibet' Silk Road city 'under threat' Muslim states 'silent' on Uighurs Uighurs blame 'ethnic hatred' Videos: China's 'Go West' policy Fear on Urumqi's streets Xinjiang under martial law China's changing approach to reporting Xinjiang Uighur leader speaks out Exiled Uighur denies stirring unrest Uighur culture under threat More than 1,000 people are reported to have been arrested and on Wednesday a senior official warned that anyone found guilty of murder would be executed. "To those who committed crimes with cruel means, we will execute them," Li Zhi, the Communist party chief for Urumqi, told reporters. Correspondent Steve Chao, reporting from Beijing, said China's leaders appeared to be pushing for a tough response to the violence and more people were likely to be arrested in the coming days as authorities round up anyone they suspect could stir up unrest. On Thursday reports said an outspoken economist who had championed Uighur rights had disappeared after presumably being arrested by police. Friends of Ilham Tohti said he had called them earlier to say police had given him formal notice to say he would be detained. Fearful Xinjiang and the Uighurs Xinjiang is officially an autonomous region in China's west. Region is sparsely populated but has large reserves of oil, gas and minerals. Xinjiang was formerly a key transit point on the ancient Silk Road linking China to Europe. Region's Turkic speaking Uighur population number around eight million. Uighur activists say migration from other parts of China is part of official effort to dilute Uighur culture in their own land. Uighurs say they face repression on a range of fronts, including bans on the teaching of their language. Uighur separatists have staged series of low-level attacks since early 1990s. China says Uighur separatists are terrorists and linked to al-Qaeda. On Wednesday Hu Jintao, the Chinese president, cut short a visit to the G8 summit in Italy, returning home to personally oversee the government's handling of the crisis. Since Sunday's riot tensions have remained high in Urumqi with mobs wielding makeshift weapons roaming the city and many residents fearful for their safety. On Tuesday thousands of Han Chinese rampaged through Urumqi's streets, smashing Uighur-owned shops and stalls and calling for revenge against the Uighurs who they say started the unrest. Groups of Uighurs also took to the streets and government forces fired tear gas at the crowds before ordering the curfew in an effort to maintain control of the city. Chinese authorities have blamed Uighurs protesters for Sunday's unrest, but have also condemned members of the Han Chinese community for stirring up tensions in the wake of the riot. Repression Uighur groups say repressive policies by China combined with years of mass migration to Xinjiang by Han Chinese, China's largest ethnic group, have stoked ethnic tensions and sown the seeds for violence. The Turkic-speaking Uighurs have long complained of repression and discrimination under Chinese rule, but Beijing insists it has brought prosperity to Xinjiang, a region that has seen annual growth rates of up to 17 per cent in recent years. On Wednesday, Recep Tayyip Erdogan, Turkey's prime minister, called for an end to the violence. "Our expectation is for these incidents that have reached the level of savagery to be rapidly stopped," he said. The prime minister and Ahmet Davutoglu, Turkey's foreign minister, made separate calls to China to bring "those responsible to account" in a transparent manner. "We are following the events with great concern, worry and sadness," Erdogan said According to Chinese state media, Sunday's clashes erupted after a demonstration over an industrial dispute in southern China in which two Uighurs died, turned violent. Beijing singled out Rebiya Kadeer, head of the World Uighur Congress, for "masterminding" the unrest. But Kadeer, a Uighur businesswoman who was jailed for years in China before being released into exile in the US, has rejected the accusations, saying from Washington DC that they were "completely false".