The attack took place on Monday in the Tahtakoruk district of Xinjiang's Kashgar city, an RFA Uyghur service said.
It, however, quoted an unnamed retired government worker as saying that he had heard from a police officer that "28 people were killed in the incident, including six attackers and three police, while the others were all bystanders."
"It seems the police who arrived at the spot were either panicked or encouraged by the 'strike hard' policy, because they opened fire indiscriminately and many people who were not linked to the attackers got killed," he said.
Xinjiang, which is on the boil over opposition from Uyghur Muslims over increasing settlements of Hans from mainland China, is experiencing a spate of terror attacks allegedly by East Turkistan Islamic Movement for the past several years.
The attack began when a car sped through a traffic checkpoint without stopping, said Turghun Memet, an officer with the nearby Heyhag district police station, according to the report.
"When one of the policemen at the checkpoint ran out of the booth, the car backed up, hitting him and breaking his leg," Memet said.
The remaining traffic police, who did not carry guns, called for backup.
"By the time armed police reached the scene, three more suspects had arrived by sidecar motorcycle and attacked the checkpoint and police cars with explosives, killing one regular police officer, another traffic policeman and one auxiliary officer," Memet said.
"They also injured four other officers and damaged a police vehicle," he said.
The report quoted another unnamed government worker as saying that the attack may have been prompted by the restrictions imposed by authorities during Ramazan.
"I think this is the first reaction to this year's Ramazan restrictions," he said.
Terrorists previously have attacked train stations, police and government buildings, mostly in Xinjiang, throwing bombs at police cars and running over civilians with vehicles.
Xinjiang police cracked down on 181 terror groups in 2014 and 96 per cent of terrorist plots were disrupted at an early stage, the local government said earlier this month.
