Unidentified assailants have attacked a border post in Xingjiang province, northwest China, four days before the Beijing Olympics.
At least sixteen police officers have been killed and around twelve more injured in the incident in the town of Kashgar.
The attackers drove up to the post and threw two grenades. A Chinese news agency says two people have been arrested.
A militant Islamist group from the region claimed responsibility for a series of bombings recently which killed five people.
The group calling itself the Turkistan Islamic Party promised to carry out attacks on the Olympic Games.
Xinjiang is home to the Muslim Uighur people, many of whom are angry at strict Chinese rule.
Some Uigur groups are campaigning for an independent homeland.
In the past few months, Chinese police have reportedly detained around eighty people in Xinjiang for plotting to sabotage the Games.