Former Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE said in a new interview that ISIS will become stronger in northern Syria and Iraq if U.S.-aligned forces do not maintain pressure in the region.

In an interview airing Sunday on "Meet the Press," Mattis warned that the region was in "disarray" due to the invasion of Turkish forces and withdrawal of U.S. troops, which he warned would benefit ISIS forces thought to be hiding in the region as well as those already detained in prison camps.

"It’s in a situation of disarray right now," Mattis said of the northern Syria region currently besieged by Turkish forces. "Obviously, the Kurds are adapting to the Turkish attacks. And we'll have to see if they're able to maintain the fight against ISIS. It's going to have an impact. The question is, how much?"

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"I think Secretary of State [Mike] Pompeo, the intelligence services, the foreign countries that are working with us have it about right that ISIS is not defeated," Mattis continued. "We have got to keep the pressure on ISIS so they don't recover. We may want a war over. We may even declare it over."

Mattis also likened President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's announcement early this week that the U.S. would allow Turkish military action in the region to former President Obama's drawdown of troops in Iraq.

"You can pull your troops out, as President Obama learned the hard way, out of Iraq, but the 'enemy gets the vote,' we say in the military," Mattis said. "And in this case, if we don't keep the pressure on, then ISIS will resurge. It's absolutely a given that they will come back."

Mattis joined a number of lawmakers on Capitol Hill this week who warned that ISIS forces in the region would capitalize on chaos caused by the withdrawal of U.S. troops and the invasion of Turkish forces. Thousands of Kurdish civilians have fled the region due to Turkish military strikes.

Trump has faced mounting Republican criticism over the issue even as his administration battles Democrats on an impeachment inquiry and a wide range of investigations.

On Monday, Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellDemocratic senator to party: 'A little message discipline wouldn't kill us' House to vote on resolution affirming peaceful transition of power Republican lawyers brush off Trump's election comments MORE (R-Ky.) urged the president to reconsider in a rare public rebuke.

"I urge the President to exercise American leadership to keep together our multinational coalition to defeat ISIS and prevent significant conflict between our NATO ally Turkey and our local Syrian counterterrorism partners," he said.