"Police officers at the scene shot dead dozens of members of the mob," the report added.
"Initial investigation showed that it was a premeditated terror attack," it said.
Beijing commonly blames separatists from Xinjiang for carrying out terror attacks which have grown in scale over the last year and spread outside the restive region.
Among the most shocking incidents was a market attack in Xinjiang's capital Urumqi in which 39 people were killed in May, and a deadly rampage by knife-wielding assailants at a train station at Kunming in China's southwest in March, which left 29 dead.
Rights groups accuse China's government of cultural and religious repression they say fuels unrest in Xinjiang.
Beijing argues it has boosted economic development in the area and that it upholds minority rights in a country with 56 recognised ethnic groups.