Tianshan, the Xinjiang government's official news portal, said 14 of the dead in the Sunday fighting near the town of Kashgar were "violent assailants," the South China Morning Post reported.
The Tianshan news website said the clashes began after local police, who were trying to arrest suspects in another incident, were ambushed by bomb-throwing, machete-wielding assailants.
Tianshan said the incident was a "terrorist attack" but didn't identify the ethnicity of the alleged attackers, CNN reported.
The Xinjiang-Uighur region is close to the border with Pakistan and Afghanistan.
Muslim Uighurs, a Turkic-speaking minority in China, resent being ruled by the majority Han Chinese. China maintains foreign Uighur groups linked to the East Turkistan Islamic Movement are to blame for much trouble in the region but the World Uighur Congress, based in Stockholm, Sweden, disputes the allegation.
International human rights groups have said China has heavy-handed security policies in Xinjiang that create ethnic tensions.
In October, Chinese authorities blamed Uighurs for a fiery vehicle crash that killed five people and injured 40 in Beijing's Tiananmen Square.
In 2009, riots killed about 200 people in Urumqi, capital of the Xinjiang region.