Sen. John McCain (R-Ariz.), returning from a recent trip to the region, told reporters that members of the Syrian Opposition Council expressed concern about the growing influence militant groups were having among rebel forces.
The problem facing the council, which the White House recognizes as the legitimate ruling authority in Syria, is how to rein in the influence of groups like the al Qaeda-affiliated Al Nusra Front in Syria, while they continue to rack up victories against Assad's forces.
"The fact is, they are viewed as the best fighters," McCain said. "And more and more of them are pouring in from literally all over the world, not just the Arab world, but all over the world."
The meeting in Cairo was part of a longer congressional visit to the region by McCain, and Sens. Kelly Ayotte (R-N.H.), Richard Blumenthal (D-Conn.), Chris Coons (D-Del.), and Sheldon Whitehouse (D-R.I.).
Along with the stop in Egypt, the group also met with regional leaders in Afghanistan and Israel. The lawmakers also visited Syrian refugee camps in Jordan.
The growing influence of Islamic radicals within Syria has also been hastened by the Obama administration to provide arms and military support to the Free Syria Army and other rebel factions battling Assad's forcess, according to the lawmakers.
McCain, Ayotte and others have been at the forefront of the GOP push to allow U.S. weapons and equipment to make their way into rebel hands. Other Gulf states have already begun to arm Syrian rebel forces, reportedly with the support of U.S. intelligence.
Publicly, the White House and the Pentagon have been adamantly opposed to arming anti-government troops directly, fearing U.S. weapons could end up in the hands of al Qaeda or other Islamic radicalist fighters who have worked their way into the rebel ranks.
However, with the nearly two-year Syrian civil war approaching a critical juncture, Whitehouse noted that in order to keep up the pressure on Assad, rebel fighters needed weapons and equipment -- regardless of whether they come from the United States or al Qaeda.
"This is a country that will remember that we were there when we needed them," he said during the Tuesday press conference. "If we don't take this step, we cede that role to these terrorists and jihadists, and that would be, I think, a real shame."
That lack of U.S. support could also create a repeat of the postwar situation in Libya, where al Qaeda-affiliated groups were able smuggle out a number of heavy weapons out of the country's military arsenals after the death of former Libyan dictator Moammar Gadhafi, Ayotte said at the same press briefing.
With Assad's vast stockpiles of chemical weapons, the United States must play a role in ensuring those weapons do not find their way into extremists' hands.
"We don't need [U.S.] boots on the ground to do that if we are involved and engaged with the right people," Ayotte said. "And that's important for the whole security of the area."