They arrested suspects and seized guns, knives, explosives and materials advocating violence and terrorism, Xinhua said.
In a new twist on Monday, China publicised letters condemning the violence addressed to victims of the riots and Rebiya Kadeer, an Uighur millionaire-turned-activist who heads the separatist World Uighur Congress. The letters, reportedly written by Kadeer's children and relatives urge locals not to believe her.
Kadeer, a mother of 11, is exiled in Washington since 2005 after serving a prison term in China. She is officially blamed as the 'mastermind' of the July 5 riots that killed 197 in the Xinjiang capital of Urumqi. Kadeer denied the charges.
The maximum riot fatalities were Han Chinese, the dominant migrant community in oil-rich Xinjiang that covers one-sixth of China and also borders parts of India, Pakistan and Afghanistan. Sections of the Uighurs, a Turkic-speaking Islamic ethnic minority of eight million in Xinjiang, have been campaigning against government controls on their religious and cultural rights.
The text of the letters is similar to the government's current propaganda of ethnic harmony. "The Government treats us very nicely," the letter reportedly said, and referred to preferential policies, new buildings and millionaire Uighurs.
"Because of you, so many innocent people lost their lives...so many houses, shops and vehicles were burnt," Kadeer's family wrote, according to the State-run agency Xinhua. "The harmony and unity among ethnic groups was undermined.''
"It's not possible one of her family members would write such a letter," spokesman of the World Uighur Congress, Dilxat Raxit, told Reuters. The mass arrests since the riots have crossed 1, 500, including 319 arrests announced on Sunday. The 319 people were detained based on 'information from the public and police investigation'. Since the riots, the public security bureau of Xinjiang has issued notices asking people to turn in suspects.