Police shot and killed four suspects after "an eruption of violence" injured more than 10 pedestrians and police in China's volatile northwest Sunday, a state media report said a day after clashes in the same Silk Road city killed seven people.

Xinhua News Agency gave few details about Sunday's fresh violence in Xinjiang, a region rocked by riots and ethnic violence in recent years.

It was unclear who started the two clashes in the city of Kashgar. But an overseas ethnic activist group said Sunday it feared the violence could prompt a fresh crackdown on minority Uighurs blamed for previous violence in the region.

A man reached Sunday at a hotel close to a major shopping street in Kashgar said he had heard what he thought were gunshots in the area in the afternoon. The staff member, who would not give his name out of fear of reprisals, said he saw police, fire engines and ambulances, which were carrying at least two injured. He said police were not allowing people or vehicles to enter the street.

An official at the Kashgar Public Security Bureau, who refused to give her name, said they had received no information about any incident Sunday afternoon.

Phone calls to the Kashgar city government and Xinjiang regional government went unanswered.

On Saturday night, two knife-wielding men hijacked a truck in the city, then rammed the vehicle into a crowd and got out to attack the pedestrians, a police official said earlier Sunday.

The attackers' identities and motive were unclear.

Xinhua reported that two blasts were heard about an hour before the incident Saturday night _ one from a minivan and the other from the food stall-lined street where the hijacking took place. The police official, from the information office of the Xinjiang regional public security bureau, said she could not confirm whether there were explosions.

According to the official, two men hijacked a truck and stabbed the driver to death. The men then drove the truck into a crowd, got out of the vehicle and attacked people along the road with a knife or knives, said the official, who also refused to give her name, as is common with Chinese officials.

People who came under attack retaliated, and one of the suspects was killed and the other caught, the official said.

A total of seven people died and 22 were injured, she said. Xinhua said six bystanders and one suspect were killed.

The official said the case was under investigation and that the motive was unclear.

Xinjiang has been beset by ethnic conflict and a sometimes-violent separatist movement by Uighurs, a largely Muslim ethnic group that sees Xinjiang as its homeland. Many Uighurs say they have been marginalized as more and more majority Han Chinese move into the region.

An overseas Uighur advocacy group said that according to information received from Uighurs in Kashgar, most of Saturday's dead and injured were members of a security force that helps the police maintain order.

"I am worried that authorities may detain more Uighurs by making use of this incident," Dilxat Raxit, spokesman for the Germany-based World Uyghur Congress, said in an email to The Associated Press.

In another violent incident less than two weeks ago, police shot 14 rioters who attacked a police station and killed four people in Hotan city, 300 miles (500 kilometers) southeast of Kashgar on July 18, Xinhua said.

In 2009, nearly 200 people in the region were killed in fighting between Uighurs and Han Chinese.

Xinjiang is China's Central Asian frontier, bordering Pakistan, Afghanistan, Russia and other countries. Kashgar was an important hub on the ancient route through which Chinese silk and other goods reached Europe.

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AP researcher Henry Hou contributed to this report.