Brett McGurk, the State Department’s senior envoy to the anti-Islamic State coalition, said that steps President Trump has taken, including delegating decision-making authority down from the White House to commanders in the field, have “dramatically accelerated” gains against the militants.

Combined Islamic State losses in both countries since the group’s peak control in early 2015 total about 27,000 square miles of territory — 78 percent of militant holdings in Iraq and 58 percent in Syria. About 8,000 square miles have been reclaimed under Trump, McGurk said in a briefing for reporters.

He said the Islamic State has been driven out of 45 percent of Raqqa, the group’s de facto Syrian capital since the launch of an offensive by U.S.-backed local forces two months ago. U.S. and coalition airstrikes have been instrumental in the ground successes of the Syrian Democratic Forces, composed of Kurdish and Arab fighters.