Weekend violence in China’s restive Xinjiang region left as many as 15 people dead, including three killed during or after a bombing attack Sunday afternoon and four attackers shot dead an hour later by Chinese security forces, according to official news agency accounts and residents reached by telephone.

The Sunday violence follows an incident reported late Saturday, when two bombs exploded, and two assailants reportedly hijacked a truck, stabbing the driver and ramming the vehicle into a crowd of pedestrians, killing seven people and injuring 22. The crowd reportedly killed one of the hijackers.

The violence occurred in the border town of Kashgar, the old Silk Road city in far Western Xinjiang near the border with Tajikistan.

Details were still emerging late Sunday, but security officials blamed the upsurge of violence on “rioters,” the term often used for Xinjiang’s Muslim Uigher separatists who have staged mostly low-level attacks against Chinese government rule. n one of the most brazen attacks, assailants stormed a police station July 18 in Hotan city and took hostages, killing four people before police in turn killed 14 of the attackers, although Uigher exile groups dispute that account of the incident.

Residents in telephone interviews and in postings on popular microblogging sites — which have become an alternative news source in China — reported Kashgar was under a strict curfew Sunday night. One resident posted on a microblog that armored vehicles had been dispatched to the area and people were remaining indoors. Some posted photos on their microblogging Weibo accounts.

Dilxat Raxit, a spokesman for the German-based World Uigher Congress, said that from his information, “a curfew was imposed on the whole city of Kashgar, and more than 100 Uighers were detained. The incident is unbelievable, but we have to face it.”

He blamed the Beijing government for the latest unrest, saying, “China must stop the long systematic policies of repression right now and withdraw the Chinese immigrants, release all the political prisoner and let the Uighers express their different views and grievances peacefully.”

The Turkic-speaking Uighers consider Xinjiang their traditional homeland, but large influxes of ethnic Han Chinese migrants over the years have left Uighers a minority. The Uighers also complain they remain economically disadvantaged, even as China overall has enjoyed double-digit growth rates and improved living standards.

Xinhua, the official Chinese news agency, said the violence Sunday began about 4:30 p.m. when a bomb exploded in downtown Kashgar. Xinhua initially reported that three people, including a police officer, were killed in the explosion, but a later Xinhua report quoted witnesses saying the three dead were “hacked to death by rioters.”

The news agency later reported that police had shot and killed four suspects after the explosion, four others were captured, and a manhunt was continuing.

The toll from 24 hours of violence would make this one of the bloodiest weekends in Xinjiang since ethnic rioting in July 2009 left nearly 200 people dead and scores of shops and businesses burned down.

Since the 2009 riots, China’s security forces have clamped down on the region, including installing scores of security cameras. But Xinjian’s Communist Party chief Zhang Chunxian, who was appointed after the riots, is trying to be seen as more open -- he started a microblog account earlier this year -- and addressing Uigher concerns, like the lack of jobs.

The latest upsurge in violence poses a challenge for the central authorities in Beijing and also for Zhang’s approach in dealing with Uigher grievances.

Raxit, the Uigher exile spokesman, said, “I'm afraid the two incidents will become a new excuse for the police to carry out further repression on Uighers.”

He also disputed the casualty toll, saying the number of Uighers killed in the unrest may be higher.

Researcher Liu Liu in Beijing contributed to this report.