Islamist separatists in western China pose the "most prominent" challenge to the country's security, economy and social stability, the China Daily newspaper quoted a top security official on Friday as saying.
Beijing has long said it faces a determined campaign by a group known as the East Turkestan Independence Movement, or ETIM, in the far western region of Xinjiang, where hundreds of people have been killed in the past few years in attacks and unrest between ethnic Uighurs and the majority Han Chinese.
"(ETIM) is the most prominent challenge to China's social stability, economic development and national security," Cheng Guoping, State Commissioner for counterterrorism and security, was quoted as saying.
The comments come about a week after a video purportedly by the Islamic State group surfaced showing Uighurs training in Iraq, vowing to plant their flag in China and saying that blood will "flow in rivers".
China is worried that Uighurs, a mostly Muslim people from Xinjiang, have gone to Syria and Iraq to fight for militant groups there, having traveled illegally via Southeast Asia and Turkey.
Rights groups say the unrest in Xinjiang is more a reaction to repressive government policies, and experts have questioned whether ETIM exists as a cohesive militant group. China denies there is any repression in Xinjiang.
Cheng said China should "closely check in on whether Afghanistan is becoming another paradise for extremist and terrorist groups. Such a major development may pose a serious challenge to the security of our northwestern border."
Last month, the Central Asia-Caucasus Analyst think-tank said in a report on its website that Chinese troops were on Afghan soil conducting joint patrols with their Afghan counterparts. China has dismissed such reports.
Security concerns have surfaced as China pursues its “One Belt, One Road” initiative to open up new land and sea routes for Chinese goods, and pours billions of dollars into investment projects around Asia, including central Asia, and beyond.
Cheng said maintaining security where there are related projects was "an important task and a demanding challenge".