He has overseen a steady increase in US troop numbers in Iraq this year.
Iraqi forces began a new attempt to recapture the town of Qaraqosh near Mosul on Saturday.
The town, which was formerly known for its large Christian population, is said to be largely empty but IS has mined the approaches to Mosul.
The militants have also been attacking with multiple suicide bombers, each driving a vehicle laden with explosives at high speed towards government lines.
Friday`s IS attack on the city of Kirkuk, 170km (105 miles) to the south-east, now appears to be over, leaving at least 35 people dead and 120 wounded, according to medical sources.
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