Vowing to plant their flag in China and that blood will “flow in rivers”, a video released this week purportedly by the Islamic State group shows ethnic Uighur fighters training in Iraq, underscoring what Beijing sees as a serious threat, Reuters reports.

China is worried that Uighurs, a mostly Muslim Turk from western China’s Xinjiang region, have gone to Syria and Iraq to fight for militant groups there, having traveled illegally via Southeast Asia and Turkey.

Islamic State claimed responsibility for the killing of a Chinese hostage in 2015, highlighting China’s concern about Uighurs it says are fighting in the Middle East.

Hundreds of people have been killed in Xinjiang in the past few years, most in unrest between Uighurs and ethnic majority Han Chinese. The government blames the unrest on Islamist militants.

The Iraqi arm of Islamic State has released a half-hour long video purportedly showing Uighurs training, as well as some images from inside Xinjiang, including Chinese police on the streets.

One shot that shows Chinese President Xi Jinping gives way to flames in front of a Chinese flag.

“Hey, brothers! Today, we are fighting with infidels across the world! I’m telling you this: Come and live here! Stay strong!,” one of the fighters says, according to Uighur speakers who analyzed the video for Reuters but declined to be identified.

“We will certainly plant our flag over America, China, Russia, and all the infidels of the world,” it says.

In another scene, a man chanting in Uighur says: “Our land of sharia has been constructed with spilt blood.”

The video then shows pictures of people who were said to have become “martyrs”, and identified as “al-Turkistānī”, or men from Turkestan, the name many Uighurs use for Xinjiang.

One of the men speaking has an accent from Yarkand, close to the old Silk Road city of Kashgar in Xinjiang’s southern Uighur heartland, one of the people who reviewed the video said.

Another fighter refers to the “evil Chinese Communist infidel lackeys”.

“In retaliation for the tears that flow from the eyes of the oppressed, we will make your blood flow in rivers, by the will of God!” he says.

Reuters was not able to independently verify the authenticity of the video.