Chinese police shot and killed 14 people during a riot near the old Silk Road city of Kashgar in which two policemen were also killed, the local government said on Monday.
The latest unrest took place in a region that has a substantial Muslim population, reports Reuters.
China has previously called some of the violence in the far western region of Xinjiang the work of Islamist militants plotting holy war.
Describing the incident which happened late on Sunday, Hua Chunying, a spokeswoman for the Ministry of Foreign Affairs, stopped short of directly blaming Islamist militants but said a "violent terror gang" attacked police with explosives.
"It once again showed the true face of violent terror. It should be condemned by all people who love peace and stability," she told a daily news briefing. "This conspiracy does not enjoy popular support and is doomed to failure."
Police were attacked by a mob throwing explosive devices and wielding knives when they went to arrest "criminal suspects" in a village near Kashgar, the regional government said.
The official Xinhua news agency said in an English-language report that "terrorists" were responsible. It did not elaborate.
A police officer reached by Reuters in the county where the incident occurred, called Shufu county in Chinese, said it was "not convenient" to provide any additional information.
Rights groups and exiles say police often use often heavy-handed tactics against the Muslim Uighur community, which calls Xinjiang home. Violence has broken out previously when groups of Uighurs protest at police stations, they say.
China has stepped up security in Xinjiang after a vehicle ploughed into tourists on the edge of Beijing's Tiananmen Square in October, killing the three people in the car and two bystanders.
China said the attack was carried out by Islamist militants, and has reacted angrily to suggestions that it was because of frustration and anger over government repression of Muslims in Xinjiang.
Many rights groups say China has long overplayed the threat posed to justify its tough controls in energy-rich Xinjiang, which lies strategically on the borders of Central Asia, India and Pakistan.