Officials say they remain confident the events will take place without incident.

“We are prepared to deal with any kind of security threat and we are confident we will have a safe and peaceful Olympic Games,” said Sun Weide, a spokesman for the Beijing organizing committee.

Officials of the International Olympic Committee said they were also confident that security in the capital would be more than adequate when the Games began. “We all feel the Chinese authorities have done everything possible to assure the safety and security of everyone attending the Games,” said Giselle Davies, a spokeswoman for the I.O.C.

According to Xinhua, two men driving a dump truck rammed it into a brigade of border patrol police officers as they jogged outside their barracks near the center of Kashgar, killing or wounding 10 officers. The attackers then jumped out of the truck, stabbing officers with knives, and then lobbed homemade bombs at the barracks, which exploded outside the compound, Xinhua said.

Officers, part of the People’s Armed Police, a paramilitary guard force, arrested the assailants, whom they described as Uighurs, ages 28 and 33, but did not release their names. Xinhua said the arm of one man was badly injured when an explosive device detonated in his hand. The police later discovered 10 more such devices and what it described as a “homemade gun” in the dump truck.

Images reportedly taken from local Kashgar television and briefly posted on the Internet showed bodies shrouded in white sheets or on stretchers. The attack, however, received no mention on the evening news in Beijing.

If the details as reported by Xinhua are accurate, the attack would be the worst eruption of ethnic violence on Chinese soil since the early 1990s, when China blamed Muslim separatists for a spate of violent attacks.

In recent years, China has waged an increasingly muscular battle against those it describes as radical Muslims. The East Turkestan Islamic Movement, a group listed as a terrorist organization by the United States and China, is blamed for much of the violence in Xinjiang. The attacks, as recounted by the Chinese government, often involve bombings of police stations, buses, factories and oil pipelines.