WASHINGTON - The U.S. military will deploy a new special operations force to Iraq to step up the fight against the Islamic State, Defense Secretary Ash Carter told Congress on Tuesday.

The introduction of the assault force puts U.S. combat troops on the ground in a more permanent role in Iraq and Syria for the first time in the year-plus fight against ISIS. It comes as some Republicans have called for more U.S. boots on the ground, while Americans stand divided.

Carter, who testified alongside Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, faced skeptical lawmakers who argued that the U.S. needed to be more forceful in countering the threat from ISIS.

Carter told the House Armed Services Committee that over time, the force would be able to conduct raids, free hostages, gather intelligence, and capture ISIS leaders. He said that would improve intelligence and generate more targets for attacks.

There are about 3,300 U.S. troops in Iraq. President Obama had previously announced he was sending fewer than 50 special operations forces to Syria.

Carter said the number in the new force would be larger than 50. He said it would be a standing force, meaning it would be stationed in Iraq. He said it would focus on helping Iraq defend its borders and build its security forces but also be in position to conduct unilateral operations into Syria.

"This is an important capability because it takes advantage of what we're good at," he said. "We're good at intelligence, we're good at mobility, we're good at surprise.

"We have the long reach that no one else has. And it puts everybody on notice in Syria. You don't know at night who's going to be coming in the window. And that's the sensation that we want all of ISIL's leadership and followers to have."

According to a U.S. official, the force could total up to a couple of hundred, including the assault teams, aviation units, and other support units. It would likely be based in Irbil.

Carter said the force might be American-only but more likely would be mixed with Kurds or others.