Former secretary of defense James Mattis on Sunday said that ISIS will "resurge" if the United States does not keep up the pressure in Syria.

"We have got to keep the pressure on ISIS so they don't recover," Mattis said on NBC's Meet the Press. "We may want a war over, we may even declare it over. You can pull your troops out, as President Obama learned the hard way, out of Iraq. But the enemy gets a vote, we say in the military."

Mattis said that unless the United States keeps pushing against ISIS, it is "absolutely a given" that the terrorist organization will come back in full force.

Mattis resigned as secretary of defense in December 2018 after President Donald Trump announced that all United States troops would be withdrawing from Syria.

As the military evacuated the region over the weekend, a number of ISIS fighters were able to escape, according to Politico.