Knife-Wielding assailants attacked a road checkpoint in China’s troubled far-west on Tuesday, killing three and taking the death toll to 31 from a surge in violence that has coincided with the Beijing Olympics, officials said.

The state-run Xinhua News Agency said an unknown number of attackers jumped from a vehicle at a road checkpoint in Yamanya town in the Muslim-dominated Xinjiang territory at about 9 am and stabbed four guards, three of whom died.

An officer who answered the telephone at Yamanya town’s police post confirmed the three deaths in the attack, though he said it occurred several hours earlier. The officer, who gave his name as Tu’ersenjiang, said the officers were local government employees who were taking down the names of people who passed through the checkpoint. They were not members of the 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.”

It was the third attack on government-linked guards this month in the troubled Muslim territory, which borders Pakistan and Afghanistan and where a militant separatist group is active.