The U.N. chief Ban Ki-Moon has arrived in Baghdad as an unprecedented standoff is underway between Iraqi troops and al-Qaeda-linked militants in western Anbar province.

Ahead of Mr. Ban’s visit on Monday, the Iraqi government said the U.N. secretary-general would discuss a number of “regional issues, especially the crisis in Syria.”

Iraqi security forces and allied Sunni tribesmen in Anbar have been battling al-Qaeda fighters from the Islamic State in Iraq and the Levant but have yet to recapture the city of Fallujah and also part of the provincial capital, Ramadi.

The extremist militants, emboldened by fellow fighters’ gains in the war in neighbouring Syria, have tried to position themselves as the champions of Iraqi Sunnis angry at the Shiite-led government over what they see as efforts to marginalise them.

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