Fifteen people have been killed and 14 others wounded in a "terrorist attack" in China's mostly Muslim Xinjiang region, the official Chinese news agency said Saturday.

A group of "terrorists" launched an attack on civilians Friday in Shache county, leaving four people dead and 14 wounded. Eleven "terrorists" were also shot dead during the violence, according to CCTV, China's state broadcaster.

Chinese state news agency Xinhua confirmed the death toll, citing a statement from local authorities.

At around 1.30pm (0530 GMT) on Friday men armed with knives threw explosive devices and attacked crowds on commercial street, Xinhua reported.

Eleven of the attackers were killed by police who were patrolling in the area. Explosives, knives and axes were seized at the scene.

The wounded were evacuated and taken to hospital, the news agency said.

Situated 200 kilometres from the regional capital of Kashgar, the district of Shache -- or Yarkand in the Uighur language -- was the scene of violent clashes in July, shortly before the end of the Islamic holy month of Ramadan.

Police officers then killed dozens of attackers "who were attacking civilians and vehicles", according to state media.

The fresh unrest underscores the deterioration of the situation in Xinjiang, where Beijing has launched a severe crackdown in recent months with dozens of executions officially announced and hundreds of arrests, followed by speedy mass trials and the public exhibition of so-called "terrorists".

Friday's attack comes five days after students of the imprisoned Uighur intellectual Ilham Tohti were brought before a Chinese court in a secret trial, accused -- like their professor -- of "separatism".

A Chinese judge Friday rejected Tohti's appeal against the life sentence imposed in September.

Tohti, a respected economist, is considered a moderate voice who had long denounced the repression of Uighurs in Xinjiang, without demanding complete independence for the region.

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Experts say that the extremely severe verdict suggests that it is unlikely that tensions will ease in Xinjiang, a vast region where violence and repression by security forces have left hundreds dead since last summer.

Xinjiang is frequently hit by unrest sparked by fierce tensions between China's ethnic Han majority and the Turkic-speaking Muslim Uighurs, with authorities regularly blaming Uighur militants for the violence.

Some Uighurs in the north west Chinese region are hostile to Beijing's leadership.

They say they are victims of discrimination and left out of the benefits of development in Xinjiang, which has seen an influx of Han Chinese moving in from elsewhere in the country.

Experts and human rights activists say that repressive policies regarding religion and culture adopted by Beijing have fuelled conflict in the region.