BEIJING -- Three knife-wielding assailants attacked staff at a Communist Party office in China's far western region of Xinjiang and set off an explosive device, killing two and injuring three others, an official news agency reported Thursday. The attackers were then shot dead by police.

The incident Wednesday afternoon was the first such publicly reported fatal attack in months in Xinjiang, where information is strictly controlled by authorities and reporting access has tightened over the past couple of years.

Authorities have blamed the attacks on radicals among the mostly Muslim, Turkic-speaking Uighur ethnic minority seeking independence from Beijing.

Three "rioters" drove into Moyu County's Communist Party courtyard in a vehicle, attacked workers with knives and detonated an explosive device, Xinhua News Agency reported, citing the Ministry of Public Security. It said an official and security guard were killed. A ministry press officer, who would only identify herself by her surname, Wang, confirmed the information in the report.

Tianshan Net, a Communist Party-run news portal in Xinjiang, had earlier said four attackers were shot dead by police and that the attack had left another person dead and three others injured.

Wang said it had taken "time to verify the situation," and declined to elaborate on the change in the number of attackers.

The attack could not be independently verified. Xinjiang has been under heavy security since deadly riots in 2009 that pitted Uighurs against ethnic Han Chinese migrants. Those measures were tightened further following a wave of attacks in Xinjiang and other parts of China blamed on Uighur separatists.

In November 2015, police killed 28 people who authorities said had killed 11 civilians and five police officers at a remote coal mine in Asku controlled by members of China's Han majority.

Some critics say the violence in Xinjiang stems from government policies that have marginalized the Uighurs, and also warn that Beijing's harsh crackdown may be radicalizing some Uighurs.

Dilxat Raxit, spokesman for the Munich-based World Uyghur Congress, which advocates Uighur rights, said authorities were provoking and suppressing Uighurs and then choosing to "suppress the resistance with violence."

"I strongly question the cause of the incident and casualty toll owing to the lack of transparent reporting in official media," he said in a statement.