Footage purportedly shows ethnic Uighurs training in Iraq and vowing to plant their flag in China.
A Daesh video released this week threatens to unleash bloody chaos in China.
In the 30-minute video, the Iraqi arm of Daesh vows to plant its flag in China and says that blood will "flow in rivers."
China has a rocky history with the Uighur population in its western Xinjiang region, which borders India, Pakistan and Afghanistan.
The government accuses militants amongst them of fanning a separatist movement and committing acts of terror. Uighurs accuse the Chinese government of systematic repression.
The video claims to show ethnic Uighurs training under Daesh in Iraq. The footage also contains some images from inside sparsely populated Xinjiang, which is China's largest administrative region.
"We will certainly plant our flag over America, China, Russia, and all the infidels of the world," the narration says.
The video was released by US-based SITE Intelligence Group, a private counter-terrorism organisation which monitors militant groups online.
Beijing has been worried that Uighurs have gone to Syria and Iraq to fight for Daesh.
China's Foreign Ministry on Wednesday said it wanted to work with the international community to fight Uighur militants, following release of the video.
Chinese Foreign Ministry spokesman Geng Shuang said he was not aware of the video and had not seen it.
"But one point is very clear. We oppose any form of terrorism and proactively participate in international cooperation to crack down on terrorism," Geng said. "We have long said that East Turkestan forces are a serious threat to China's security and we are willing to work with the international community to jointly crack down on East Turkestan separatist and terrorist forces," he said.
Beijing says foreign militants have stirred up tensions in Xinjiang, where it says it faces a campaign by separatists who want to establish an independent state called East Turkestan.
In 2015, Daesh claimed responsibility for the killing of a Chinese hostage, underscoring Beijing's concerns over the terrorist organisation.
However, many rights groups and Uighurs in exile doubt the existence of a coherent militant group in Xinjiang. They say oppressive policy over Uighurs is more to blame for the unrest.
China denies any repression in Xinjiang.