The recent detentions are said to be due to a call to the public
Chinese police have recently arrested 319 people for last month's violence in Xinjiang, according to state media.
This brings the total number of people detained over the riots to more than 1,500, although it is unclear how many people have since been released.
The violence between ethnic Uighurs and Han Chinese left almost 200 dead.
Meanwhile, Beijing has claimed that relatives of exiled Uighur activist Rebiya Kadeer have written letters criticising her over the riots.
Beijing has repeatedly blamed Mrs Kadeer - the head of the World Uighur Congress - for triggering the violence, a claim she vehemently denies.
A spokesman for the congress said the letters were fake.
The violence in Xinjiang was the worst ethnic unrest in China for decades.
It began on 5 July during a protest over a brawl in southern China in which two Uighurs were killed.
The government says 197 people died in the ensuing violence, and more than 1,700 were injured.
Rebiya Kadeer spent time in a Chinese prison before moving to the US
The government says most of the dead were Han Chinese, but the World Uighur Congress claims many Uighurs also were killed.
The 319 people who have been detained recently are in addition to 253 detentions last week and more than 1,000 before that, according to Xinhua news agency.
The most recent arrests came as a result of a call for information from the public, Xinhua said.
In the aftermath of the riots, local media published a list of wanted men and urged people to turn in suspects who were still at large.
It is unclear what proportion of those detained are Uighur or Han, or if any of them have been since charged or released.
As head of the World Uighur Congress, Mrs Kadeer is often accused by China of fomenting unrest in Xinjiang, and has been blamed for orchestrating the July riots.
According to Chinese media, Mrs Kadeer's son Khahar and daughter Roxingul, as well as her younger brother Memet, have written letters condemning their mother over the unrest.
"Because of you, many innocent people of all ethnic groups lost their lives in Urumqi on 5 July, with huge damage to property, shops and vehicles," Xinhua quotes one letter as saying.
"We want a stable and safe life
Please think about the happiness of us and your grandchildren. Don't destroy our happy life here. Don't follow the provocation from some people in other countries."
It is difficult to independently authenticate the letters, but Dilxat Raxit, a spokesman for the World Uighur Congress based in Germany, quickly rejected them as fakes.
"It's not possible that one of her family members would write such a letter," he told reporters.
Five of Mrs Kadeer's 11 children still live in Xinjiang, and according to human rights groups they have experienced many forms of harassment because of their mother.
Her eldest son, Khahar, was reportedly fined and forced to liquidate his mother's business and two other sons have been given jail terms - one for tax evasion, the other for "secessionist" activities.