Official Chinese media had earlier reported police in the region killed eight of the 11 people during an attack last Friday in Wushi County in Aksu prefecture, while the other three died by their own suicide devices. One suspect was reportedly captured.
It was the latest in a series of violent incidents that have rocked the Xinjiang region, home to the minority Muslim Uighurs, leaving dozens of people dead. As in the past, the official reports on Friday's incident did not identify the ethnicity of the victims.
The official Xinhua News Agency, reporting on the Friday incident, said Sunday police investigation showed the attack was "organized, premeditated terrorist assault targeting the police."
Xinhua quoted local police as saying the "terrorists," riding motorcycles and cars and carrying explosive devices and knives, attacked a police patrol, injuring two police officers and two civilians.
Last December, 24 people died in two separate incidents in the same region, which too were blamed on terrorists.
China maintains foreign Uighur groups linked to the East Turkistan Islamic Movement are to blame for the trouble in the region. However, the overseas-based World Uighur Congress disputes the allegations.
Advocates of Uighur self-determination and international human rights groups have said China's heavy-handed security policies in Xinjiang are only crating more ethnic tensions.