Syringe attacks carried out since Aug 20 have resulted in panic and resentment from the public, the official said.
By Thursday, local hospitals had dealt with 531 victims of hypodermic syringe stabbings, 106 of whom showed obvious signs of needle attacks.
Suspects were caught Wednesday when attacking members of the public. They were beaten by a angry crowd and one was seriously injured.
Five people have been confirmed dead and 14 others injured and hospitalized following Thursday's protests, Zhang said.
Of the five dead, two had been confirmed as innocent civilians, while police are trying to identify the remaining three.
Investigation had showed those involved in the syringe attacks were from the Uygur ethnic group while those attacked included people from Han and other ethnic groups.
Xinjiang police has captured 25 syringe attackers, of whom seven are in police custody, four were arrested and four others were referred for criminal prosecution, the Xinjiang regional government sources said Friday.
"The 'three forces' (separatism, terrorism and extremism) at home and abroad are not willing to see ethnic unity and their failure when the July 5 violence died down quickly," he said. "So they are using 'soft violence' to disrupt social order and instigate ethnic hatred."