Though details are sketchy because much of the information is tightly controlled by the Chinese government, the BBC said more than 100 people riding motorcycles, some wielding knives, attacked a police station in the desert city Hotan Friday. The attack came a day after clashes in another part of the region killed 35 people.
Xinjiang borders central Asia and its population is 45 percent Uighur Muslims -- a group that's been increasingly marginalized as ethnic Chinese flood into the region.
Yu Zhengsheng, a member of the ruling Communist Party's standing committee, said security in the region is being expanded.
"We will step up actions to crack down upon terrorist groups and extremist organizations and track the wanted," Yu said.
China's official Xinhua news agency said President Xi Jinping, at a security meeting, personally ordered the military to restore order in Xinjiang.
Xinhua blamed forces "in and outside the country" for the violence.