Defense Secretary Jim Mattis is crediting changes in tactics ordered by President Trump for increasing the pressure on the Islamic State in Iraq and Syria, and leaving the beleaguered fighters with no avenue of escape.

"He directed a tactical shift from shoving ISIS out of safe locations in an attrition fight to surrounding the enemy in their strongholds so we can annihilate ISIS," Mattis said Friday during a Pentagon briefing on the counter-ISIS campaign.

Mattis said that by making sure foreign fighters can't get away, or return to their home countries, "We don't simply transplant this problem from one place to another."

Joint Chiefs Chairman Gen. Joseph Dunford pointed to two other changes that came as result of the president's direction to accelerate the defeat of ISIS, including allowing U.S. advisers to accompany partner forces closer to the front lines, and the decision to arm Syrian Kurds to facilitate the liberation of Raqqa, the Islamic State's self-proclaimed capital in Syria.

The Pentagon says since the campaign against ISIS began in 2014, the terror group has lost more than 20,000 square miles of territory and 4.1 million people have been freed from the brutal grip of ISIS rule.

Mattis and Dunford also disputed reports that suggested that by waiting until now to approve a Pentagon plan to arm Syrian Kurds, the Trump administration in any way delayed the siege of Raqqa.

The only thing that has delayed the coming offensive, said Mattis, was the vagaries of the battlefield.

Mattis said the defeat of ISIS is a foregone conclusion.

"West Mosul, in accordance with tactics changed by President Trump, is surrounded, and our Iraqi partners are in a stiff fight," Mattis said. "There is no escape for ISIS."