The head of a China's largest mosque was murdered after conducting morning prayers, the local government in the far western region of Xinjiang said Thursday, amid intensifying violence in the turbulent region.

Jume Tahir, the government-appointed imam of the 600-year-old Id Kah mosque in the city of Kashgar, was killed Wednesday by "three thugs influenced by religious extremist ideology", the Xinjiang government web portal Tianshan said.

Police launched an all-out investigation and shot dead two of the alleged assailants while capturing the other, Tianshan said.

Tianshan said Tahir's killing was "premeditated" and that the suspects intended to commit a "ruthless murder".

It also said they wanted to "increase their influence via 'doing something big'".

Tahir was found dead in a pool of blood outside the mosque's prayer house, Radio Free Asia (RFA) reported earlier on its website.

Xinjiang, home to China's mostly Muslim Uighur ethnic minority, has seen escalating violence which in the past year has spilled over into other parts of China.

RFA cited what it described as "witnesses and other officials", including the director of a neighbourhood stability committee in Kashgar, who described the killing as an assassination.

Imams and other religious leaders in China are appointed by the government and subject to strict control on the content of their preaching.

US-based RFA said that Tahir had been critical of violence carried out by Uighurs, and China's official Xinhua news agency in early July quoted him as condemning terrorist violence carried out in the name of ethnicity and religion.

Dilxat Raxit, spokesman for the exiled World Uyghur Congress (WUC), did not condemn the killing.

"Chinese policies in the area have caused things to happen which should not happen," he told AFP in an email.

"According to local Uighurs, Jume Tahir consistently co-operated with the government, aided the monitoring of religious activities, and used his position in the mosque to promote Chinese policies which are unacceptable to Uighurs," he said.

"Local Uighurs suspected he had a special relationship with the Chinese ministry of security."

The Id Kah mosque is said to have a capacity of up to 20,000 people.

Kashgar, where the mosque is located, is an old oasis city that was part of the Silk Road trade route that ran from Europe to Asia.

The killing came two days after dozens of people died in violence between Uighurs and security authorities in the Kashgar region.