Clashes left a dozen people dead in a region of northwestern China that sees periodic violence between Muslim Uighurs and majority Han Chinese, with the latest unrest flaring at a sensitive time just ahead of the national legislature.

The bloodshed late Tuesday in the Xinjiang region's Yecheng county was triggered by what state media called either "rioters" or "terrorists" with knives who killed 10 people. Police fatally shot two of the assailants, the reports said.

A spokesman for an overseas Uighur group described the violence as a clash between local Uighurs and armed Chinese security personnel.

The government has failed to win over Uighurs and other ethnic minorities through policies to boost economic growth and incomes as it increases police presence and controls religious practices to deter displays of separatism. China's ethnic Tibetan regions have also been unsettled in recent months by scattered demonstrations and clashes with authorities, as well as monks and nuns setting themselves on fire in protest against the government's policies.

The national legislature's annual session opens next week, and security is being tightened across the country.

The Xinhua News Agency said the rioters attacked victims with knives in Yecheng county, about 155 miles (250 kilometers) southeast of the city of Kashgar, starting at about 6 p.m. They killed 10 people and police shot two assailants to death, the report said.

Xinhua said police were chasing others involved in the attacks but did not say how many suspects there were.

A Communist Party official in Yecheng county, who declined to give his name, later said that all the rioters had been captured by police, but he refused to answer further questions. Calls to police offices in Yecheng went unanswered.

Dilxat Raxit, a spokesman for the German-based World Uyghur Congress, said that local Uighurs told him seven armed Chinese security personnel were killed and three people were shot to death. He said two additional people were killed but did not provide any detail of those deaths. He said 10 people were injured, including two seriously hurt, and police have detained 84 people. Police have sealed off the area, he said.

Dilxat said the violence in Yecheng - which Uighurs call Kargilik - erupted because local residents "could no longer bear China's systematic repression," and have been denied outlets for peaceful protest.

Censors blocked postings about the attack on Twitter-like microblogs. Searches on Sina Corporation's popular Weibo service returned the message: "In accordance with relevant laws, regulations and policies, 'Xinjiang Yecheng' search results were not shown."

Periodic attacks occur in Xinjiang despite a smothering security presence imposed following 2009 riots in the regional capital of Urumqi that left almost 200 people dead. The riots pitted Uighurs against migrants from China's majority Han.

Xinjiang saw more deadly violence last summer, when a group of Uighurs stormed a police station in the city of Hotan on July 18 and took hostages, killing four. On July 30 and 31, Uighurs in Kashgar hijacked a truck, set a restaurant on fire and stabbed people in the street. Authorities said 14 of the attackers were shot by police in Hotan, and five assailants were killed in the violence in Kashgar.

China says those events were organized terror attacks, but an overseas Uighur rights group says they were anti-government riots carried out by angry citizens. Uighur (pronounced WEE'-gur) activists and security analysts blame the violence on economic marginalization and restrictions on Uighur culture and the Muslim religion that are breeding frustration and anger among young Uighurs.

Chinese authorities have offered little evidence to back up their claims of outside involvement and rarely provide details on arrests or punishment of the suspects. Tight information controls and the remoteness of the area, more than 2,175 miles (3,500 kilometers) west of Beijing, ensure that the circumstances surrounding such incidents often remain murky.