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The U.S. will send a small number of U.S. special operations forces into Syria as part of a shift in its strategy against ISIS, White House officials announced Friday.

President Barack Obama has authorized a contingent of fewer than 50 commandos to deploy into northern Syria and work with moderate opposition forces who are fighting the militants.

While the White House has consistently said it would not put U.S. boots on the ground, spokesman Josh Earnest insisted that they will be there in a “train, advise and assist mission” — and not in a combat role.

“It will not be their responsibility to lead the charge up the hill,” he said. But he acknowledged they will be in a perilous situation: “There is no denying the amount of risk they are taking on here.”

Related: Pentagon Ends Program to Train Syrian Rebels

Earnest called the additional forces an “expansion” but not a “change” in U.S. strategy against ISIS. He was unable to detail what the special operators will do, citing security concerns.

He also didn’t deny the suggestion that the increase in forces would not turn the situation around in Syria, where President Bashar Assad remains in power.

Obama “has been quite clear that there is no military solution to the problems that are plaguing Iraq and Syria — it’s a diplomatic one,” Earnest said.

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A senior U.S. official earlier told NBC News that the special operations forces will work alongside groups with a "proven track record" of fighting ISIS.

That could include working with Kurdish and allied actors who have come together under the umbrella of the "Syrian Democratic Forces," the official said, speaking on condition of anonymity before the announcement was made.

Rep. Mac Thornberry, chair of the House Armed Services Committee, said the expected announcement made clear the White House was feeling the pressure of a "failed policy" against ISIS.

"I'm concerned that the administration is trying to put in place limited measures — too late — that are not going to make a difference," he told NBC News. "I don't see a strategy towards accomplishing a goal, I see an effort to run out the clock without disaster."

Obama and his administration have come under mounting pressure amid signs the anti-ISIS coalition has stalled or at least failed to turn the tide against the militants — including the recent Pentagon decision to abandon a failed program to train and equip Syrian rebels.

Small signs of a sea change in strategy have been filtering out in recent weeks and gained steam in the wake of a U.S.-backed raid to free ISIS hostages that cost the life of a Delta Force commando.

Defense Secretary Ash Carter warned earlier this week that to expect more such raids when he told the Senate Armed Services Committee that the Pentagon would be stepping up attacks against ISIS — including through "direct action on the ground" in Iraq and Syria.

Carter's remarks — in testimony to the Senate Armed Services Committee — immediately raised eyebrows given repeated assurances from Obama that U.S. troops in the region would not engage in combat.

The defense secretary himself referred to the aforementioned raid as "combat," where "things are complicated," in his comments to the committee.

After news of the announcement first leaked, at least one member of the Senate Armed Services Committee questioned how Congress has "failed" to perform one of its most fundamental duties — to debate and vote on the authorization of military force.

"The decision of whether to place citizens in harm’s way in defense of this nation — to declare war — must be made by the people through their elected representatives," Sen. Tim Kaine, D-Va., said in a statement. "It is time for Congress to do its most solemn job — to debate and declare war."

Earnest said at Friday’s news briefing that Congress had already given the executive branch in 2001 the right to take action in fighting terrorists. In addition, he said, the Obama administration has been pushing this year for Congress to take up legislation that authorizes the U.S. to formally fight ISIS, but lawmakers have been skeptical.

The U.S. currently has around 3,300 troops in Iraq to train and advise Iraqi forces and protect U.S. facilities.

Earnest said Friday that Obama spoke with Iraqi Prime Minister Haider al-Abadi by telephone earlier to assure him of the U.S.'s commitment to destroying ISIS. He added that it was too soon to announce whether the U.S. would increase the special operations forces in Iraq as it is doing in Syria.

"I certainly wouldn’t rule out something like that could be a possibility if it continues to be an element of our strategy" that works, Earnest said.