WASHINGTON - New approaches approved by President Trump to defeat Islamic State militants have begun to bear fruit, Defense Secretary Jim Mattis told reporters Friday.

Commanders in the field have been given greater authority to press the fight without approval from Washington, and a tactical shift to "annihilation" from a war of attrition has thrown fighters from the Islamic State, or ISIS, on "their back foot," Mattis said.

Brett McGurk, special presidential envoy for the Global Coalition to Counter ISIS, left, and ...more
Brett McGurk, special presidential envoy for the Global Coalition to Counter ISIS, left, and Defense Secretary Jim Mattis listen during a news conference at the Pentagon on May 19, 2017.
Jacquelyn Martin, AP

"We're there to drive ISIS to its knees," Mattis said.

A military analyst, however, cautioned that the threat from extremists won't end even if ISIS is destroyed, and that good governments are key to stability in the region.

Mattis, along with Marine Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, and Brett McGurk, the presidential envoy to the coalition fighting ISIS, gave a generally upbeat assessment of the fight that began in 2014. That's when a U.S.-led coalition, mostly using warplanes, began pounding ISIS fighters who had gobbled up large chunks of Iraq and Syria in a largely uncontested fight. There are now thousands of U.S. troops on the ground in Iraq and Syria, mostly as advisers.