Washington (CNN) U.S. Gen. Paul Selva withstood one of the most biting rebuttals of the country's ISIS strategy Wednesday when he told lawmakers the Pentagon would not impose a no-fly zone on Syria because of possible blowback from Russia and Syria.

"We have the military capacity to impose a no-fly zone. The question that we need to ask is do we have the political and policy backdrop with which to do so," Vice Chairman of the Joint Chiefs of Staff Selva told the Senate Armed Services Committee, pointing to the threat of "direct conflict" with Syrian forces or "a miscalculation" with the Russians should they challenge the no-fly zone.

Committee Chairman John McCain, an Arizona Republican, shot back: "I must say, it's one of the more embarrassing statements I've ever heard from a uniformed military officer, that we are worried about Syria and Russia's reaction to saving the lives of thousands and thousands of Syrians who are being barrel-bombed and massacred."

The exchange encapsulated a morning of tough grilling by members of the committee as Selva and Defense Secretary Ashton Carter defended the argument Obama made Sunday: the ISIS strategy is working, so give it time.

But even as Carter said that the U.S. is "building momentum against ISIL," also known as ISIS, he agreed with an assessment from McCain that the terrorist group hadn't been contained. That contrasts with what President Barack Obama said had been achieved against the organization last month.

Republican members of the panel were impatient, demanding to know how the U.S. would train Syrian forces and why the administration had not enlisted the aid of Arab allies who could provide ground forces.

But even as they were on the defensive, Pentagon officials offered some news of expanding the fight against ISIS, saying they were likely to provide Apache helicopters to Iraqi forces looking to retake Ramadi from ISIS and said they were close to securing special forces help from Arab allies.

More U.S. support on the ground?

Carter raised the prospect Wednesday that U.S. military advisers could accompany Iraqi forces on the ground in the effort to take back Ramadi.

A U.S. official told CNN that any advisers accompanying Iraqi forces would likely stay back from the front line of combat. The official said those helicopters would likely be Apaches.

But the White House cautioned later in the day that nothing was final yet. White House Press Secretary Josh Earnest said Obama has not yet signed off on the Apaches and they would only be used at the request of Iraq Prime Minister Haider al-Abadi.

On Tuesday, Iraqi officials said the Iraqi Security Forces have taken back 60% of Ramadi from ISIS. A U.S. official who spoke to CNN, however, disagreed with that assessment, saying, "they have made some progress, but not that much."

Carter's pitch to lawmakers came a few days after Obama delivered a prime time address looking to reassure Americans that his plan for ISIS is working. Carter largely recounted the administration's efforts so far, but he also asked lawmakers to release $116 million in funding for U.S.-backed forces.

Following a testy exchange with Carter, South Carolina Sen. Lindsey Graham pressed his case for a more expansive authorization of military force for the U.S. effort against ISIS.

"Mr. President, are you all in or not?" asked Graham, who is seeking the 2016 Republican nomination.

Carter defended a three-year time limit in the current authorization and other constraints, as Graham pressed for support of his positions.

"To the Congress: If you don't like what this president or a future president does, in terms of fighting ISIS, defund it. That's your job," Graham said, before turning back to the White House. "I am making a simple proposition to this president that I will give you whatever you need in terms of my authorization to go wherever you need to go as long as it takes to use whatever available tools you have within legal limits to destroy this threat."

The Senate hearing came two days after Joint Chiefs Chairman Gen. Joseph Dunford said that U.S. allies are close to sending their own special forces to the region to aid in the fight against ISIS.

"Although I can't talk to you about the countries right now, because we are still in the process of discussing with them, we have a number of other countries that we are working with right now to provide additional special operations in Syria and Iraq," Dunford told U.S. forces in Bahrain Monday during a USO tour of military facilities before the holidays.

Dunford's comments were first reported by Stars and Stripes.

A U.S. official told CNN the U.S. would like to see special operations forces from the United Kingdom and France take part in the battle against ISIS.

FBI on working with Muslims

At the same time Carter and Selva were testifying, FBI Director James Comey was discussing the recent terror attack in San Bernardino shooters just one floor above them.

At the Senate Judiciary Committee's oversight hearing of the FBI, Graham asked Comey if suggestions that all Muslims should be banned from entering the U.S. harms the FBI's ability to fight terrorism.

GOP presidential front-runner Donald Trump has called for all Muslim immigrants to be banned from the United States, warning that there will be additional terror attacks in the U.S. if his temporary ban is not put in place.

Comey said he did not want to "take shots" at any particular presidential candidate, but said estranging Muslims makes the FBI's work difficult.

"I do believe that our ability to get cooperation in the Untied States depend upon people trusting us and having a level of comfort with us, and estrangement gets in the way of that," Comey said.

Comey said that terrorists groups often portray the U.S. as anti-Muslim in its recruitment.

'The notion that the U.S is anti-Muslim is part of ISIS's narrative, al-Qaeda's narrative and other terrorist groups,' he said.