The US has urged China to conduct a transparent investigation after clashes in the restive Xinjiang region left 21 people dead.
US State Department spokesman Patrick Ventrell also urged that "due process protections" be given to all Chinese citizens, including ethnic Uighurs.
The violence erupted on Tuesday in Bachu county, Kashgar prefecture.
China said it was a planned attack by a "violent terrorist group", but an activist group questioned this.
"We urge the Chinese authorities to conduct a thorough and transparent investigation of this incident," Mr Ventrell said.
He asked China to provide Uighurs with all the protections "to which they are entitled not only under Chinese constitutional laws but the international human rights commitments as well".
He also called on China to safeguard religious rights.
Xinjiang officials say the clashes erupted after what they described as community workers searched homes for weapons.
Fifteens police and officials were killed, and six suspects. Another eight people were arrested.
But a spokesperson for the World Uighur Congress, an umbrella organisation of Uighur groups, said the incident was caused by the killing of a young Uighur by Chinese "armed personnel" as a result of a government clean-up campaign.
The incident come amid rumbling ethnic tensions between the Muslim Uighur and Han Chinese communities.
Uighurs make up about 45% of the region's population, but say an influx of Han Chinese residents has marginalised their traditional culture.
In 2009 almost 200 people - mostly Han Chinese - were killed after deadly rioting erupted.
Beijing authorities often blame violent incidents in Xinjiang on Uighur extremists seeking autonomy for the region. Uighur activists, meanwhile, accuse Beijing of over-exaggerating the threat to justify heavy-handed rule.
Verifying reports from Xinjiang is difficult, correspondents say.
Foreign journalists are allowed to travel to the region but frequently face intimidation and harassment when attempting to verify news of ethnic rioting or organised violence against government authorities.
An editorial in state-run China Daily on Thursday stated that there had to be "decisive moves to wipe out terrorist cells in the country".
It added that the Xinjiang incident "is another bloody reminder that terrorist threats remain a clear and present danger in the country's northwestern region".