Calls to Hotan government offices and a spokeswoman for the Xinjiang government were not answered.

The clash on Friday is likely to alarm the Chinese government. It came just two days after a confrontation in Turpan Prefecture, another part of Xinjiang, left 35 people dead, according to the state-run news agency, Xinhua. In that episode, Xinhua said, a crowd attacked a township police station and government offices on Wednesday, and the police fired on the participants. Xinhua said rioters killed 24 people, and police officers fatally shot 11 rioters.

“We’re seeing now violent instances becoming more frequent, unfortunately,” said Alim A. Seytoff, the president of the Uyghur American Association, an exiled group based in Washington that campaigns for an independent Uighur homeland, which advocates call East Turkestan. “You can see from these instances of violence the intensification of Chinese repressive rule in the region.”

The clashes this week came just before the fourth anniversary of widespread bloodshed in Urumqi, the regional capital of Xinjiang. At least 197 people were killed on July 5, 2009, after the police broke up a protest by Uighurs and the confrontation gave way to attacks by rioters on Han people, who make up China’s majority. Han Chinese protesters later marched on Uighur neighborhoods, some attacking homes with bricks and cleavers. The police never said how many died or were injured in those revenge riots.

Yang Shu, a Chinese professor who studies unrest in Xinjiang, said the recent violence reflected Uighur grievances about social inequalities and dislocation driven by economic modernization, the spreading influence of militant currents of Islam and the deterioration of ethnic relations since 2009. In July 2011, 18 people died when rioters in Hotan stormed a police station.

“The July 5 incident is a major factor,” Professor Yang, the director of the Institute for Central Asian Studies at Lanzhou University in northwest China, said in a telephone interview. “It was a watershed. Afterward, Uighur-Han relations have clearly deteriorated. We can’t avoid this problem.”