KUQA, China — Knife-wielding assailants attacked a road checkpoint in China's troubled far west today, killing three guards and raising the death toll to 31 from a surge in violence coinciding with the Beijing Olympics, officials said.

The state-run Xinhua News Agency said an unknown number of attackers jumped from a vehicle at the checkpoint in Yamanya town in Muslim-dominated Xinjiang territory and stabbed four guards, three of whom died.

It was the third attack on government-linked guards this month in Xinjiang, which borders Pakistan and Afghanistan and where an Islamic militant separatist group operates.

An officer at Yamanya town's police post confirmed the three deaths.

The officer, who gave his name as Tu'ersenjiang, said by telephone that those killed were local government employees who were taking down the names of people who passed through the checkpoint, and were not police or military.

"The case is still under investigation," Tu'ersenjiang said.

A man at the public security bureau in Shule county, where Yamanya is located, said the injured officer was in critical condition at a hospital.

"He has pulled away from danger," said the man, who refused to give his name because he was not authorized to speak to the media. "We are now waiting for him to wake up and speak so we can find out more details about what happened."

On Sunday, militants tossed homemade bombs at government buildings in Kuqa city, then fought with police. Twelve people died, officials said.

Six days earlier, assailants rammed a truck into a group of border police and then attacked them with knives and homemade bombs in Kashgar.

No one has claimed responsibility for the attacks, though government officials have suggested terrorism is behind the violence and insist it is not linked to the Olympics.

But with three audacious attacks in just more than a week and the appearance online of videos threatening the Olympics, ethnic Uighur extremists might be trying to use the games as a way to force themselves out of obscurity into the world's view.

Residents and experts say many Uighurs are seething with anger toward Chinese immigrants who are seen by many as symbols of government oppression.

Anti-government violence has flared in Xinjiang for years. But Nicholas Bequelin, a researcher with New York-based Human Rights Watch's Asia Division, said Sunday's attacks were more highly organized. Thirteen men and two women used an explosive-laden three-wheeled vehicle and lobbed bombs at 17 sites in the city in quick succession.