Muslim extremists from China's far western region of Xinjiang have gone to the Middle East for training and some may have crossed into Iraq to participate in the upsurge of violence there, China's special envoy for the Middle East said on Monday, July 28, according to Reuters.

China has repeatedly expressed concern about the upsurge in violence in Iraq and the march of the Islamic State of Iraq and the Levant (ISIS or ISIL), which has seized much of the north of the country as Baghdad's forces there collapsed.

ISIL has renamed itself the Islamic State and proclaimed the establishment of a caliphate on land it has captured in Syria and Iraq.

Wu Sike, who has recently returned from the region, told reporters that China was extremely worried about the role of extremist groups in the fighting in Syria and Iraq.

"Several hot spot issues in the Middle East have provided living space for terrorist groups, in particular the crisis in Syria has turned this country into a training ground for extremists from many countries," he said.

"These extremists come from Islamic countries, Europe, North America and China. After being immersed in extremist ideas, when they return home they will pose a severe challenge and security risk to those countries," Wu added, according toReuters.

Xinjiang, home to the Muslim Uighur people who speak a Turkic language, has been beset by unrest for years, blamed by Beijing on Islamist extremists who want to establish an independent state called East Turkestan.

While many experts outside of China doubt these groups have anywhere near the abilities Beijing accuses them of, some Uighurs have made their way to Afghanistan and Pakistan in recent years.

Wu would not put a number on how many Chinese citizens may be in the Middle East either fighting or being trained, saying that he understood from foreign media reports the figure to be about 100.

China is Iraq's largest oil client, and its state energy firms, which include PetroChina, Sinopec Group and CNOOC Ltd, together hold more than a fifth of Iraq's oil projects after securing some of its fields through auctions in 2009.

Wu, who studied in Iraq in the 1970s, said that despite the violence he was confident in the country's future and China's involvement in its energy sector.