29 July 2014 Last updated at 05:07 ET
A Chinese official says 13 people were killed on Monday in the latest outbreak of violence in the western region of Xinjiang.
The regional official told the BBC the incident took place in Yarkant, a town near the border with Tajikistan.
All the victims are understood to be Han Chinese. The area is seen as the heartland of the region's Muslim Uighur ethnic minority.
Official media and government news sources have not reported the attack.
Confirming details of incidents in Xinjiang is difficult, because the flow of information is tightly controlled.
The BBC's Damian Grammaticas says the lack of official reporting on the incident may be an attempt to prevent any worsening of ethnic or religious tensions in the area.
In 2009, large-scale ethnic rioting between Han Chinese and Uighur communities in Xinjiang's capital, Urumqi, left some 200 people - mostly Han Chinese - dead.
In recent months there has been an upsurge in Xinjiang-linked violence that authorities have attributed to Uighur separatists.
In May at least 31 people were killed when two cars crashed through an Urumqi market and explosives were thrown. In March, a mass stabbing at Kunming railway station killed 29 people.
In response Chinese authorities have launched a year-long security campaign which includes increased police and troop presence in key cities and towns in Xinjiang.
Uighur rights groups say there is considerable resentment against Chinese rule in Xinjiang, in particular restrictions on religious and cultural freedoms.
China says it is investing heavily in the region to improve people's lives.