Defense Secretary Jim Mattis said Thursday he believes Congress backs the Trump administration's effort to defeat the Islamic State following two closed-door briefings with lawmakers.

Mattis, along with Secretary of State Rex Tillerson and Joint Chiefs Chairman Gen. Joseph Dunford, spent over an hour updating House members on the campaign and what he called a growing coalition of allies.

"I have no doubt we have the support of Congress and that was loud and clear," Mattis said when leaving the meeting on Capitol Hill.

The three top Trump administration officials updated the Senate on progress Wednesday but did not deliver a new strategy against the terror group in Iraq, Syria, Afghanistan and elsewhere.

"We just gave them an update on where we're at in the defeat-ISIS campaign and the building of the defeat-ISIS international coalition, which is enlarging as you know," Mattis said.

In January, President Trump ordered the Pentagon to review Obama administration efforts when he came into office in January and report back with a new strategy within 30 days. On Thursday, he visited the Pentagon and met with Mattis, Tillerson, and other administration officials to discuss the terror group.

"We're doing very well against ISIS. ISIS is falling fast, very fast," Trump said.

But some House Democrats still had concerns following Mattis' briefing.

Rep. Adam Schiff, D-Calif., said the administration has yet to fill in its strategy for a long-term political solution after the U.S.-led coalition recently liberated Mosul and appeared to be making gains against the Islamic State in Raqqa, its de facto capital in Syria.

"I think we are certainly making progress on the battlefield but I think the political progress in Iraq had been very slow and in Syria is horribly complicated," said Schiff, who is the ranking Democrat on the House Intelligence Committee. "I think it is still very difficult to see the end game."