MOSUL, Iraq - A U.S. official says the nearly three-week offensive against Islamic State extremists in Mosul is "ahead of schedule."

Brett McGurk, the White House envoy to the U.S.-led anti-IS coalition, spoke Sunday to reporters in Jordan.

The push to drive IS out of Mosul, Iraq's second largest city, slowed in recent days. Iraqi forces have entered more densely populated areas, where they cannot rely as much on airstrikes and shelling because of the risk posed to civilians.

McGurk says the campaign to degrade the group and break up its self-declared caliphate in Syria and Iraq was expected to take about three years. The envoy says two years into the campaign, "in many ways we are ahead of where we thought we would be."