Muslim extremists from the Xinjiang Uygur autonomous region have gone to the Middle East for training and some may have crossed into Iraq to take part in the upsurge of violence there, China's special envoy for the Middle East, Wu Sike, said on Monday.

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

ISIL, alternately translated as the Islamic State of Iraq and Syria, or ISIS, has proclaimed the establishment of a caliphate on land it has captured in Syria and Iraq.