Former U.S. Defense Secretary James Mattis said ISIS “will resurge” in Syria, in his first public comments following U.S. President Donald Trump’s withdrawal of troops from the region.

“I think Secretary of State Pompeo, the intelligence services, the foreign countries that are working with us have it about right that ISIS is not defeated. We have got to keep the pressure on ISIS so they don’t recover,” Mattis said in an interview on NBC News’ “Meet the Press” set to air Sunday.