WASHINGTON - A Senate panel voted Tuesday to provide weapons to rebels battling the forces of Syrian President Bashar al-Assad, the first time lawmakers have endorsed the aggressive U.S. military step of arming the opposition.

The Foreign Relations Committee voted 15-3 for a bill that would give lethal aid and military training to vetted rebel groups, and would slap sanctions on anyone who sells oil or transfers arms to the regime.

An intense committee debate over the bill underscored congressional fears on greater involvement in a Mideast war after more than a decade of American combat in Iraq and Afghanistan. It also exposed divisions within the Republican Party about U.S. foreign policy that will remain well into the 2016 GOP presidential nomination fight.

"The greatest humanitarian crisis in the world is unfolding in and around Syria," said Sen. Robert Menendez (D., N.J.), the committee chief. ". . . The United States must play a role in tipping the scales toward opposition groups and working to build a free and democratic Syria."

Sen. Bob Corker of Tennessee, the panel's top Republican, implicitly criticized the Obama administration as he joined Menendez in embracing the measure. "Much of the policy on Syria has been done on an ad hoc basis," Corker said.

Opposing the legislation were Sens. Rand Paul (R., Ky.), a potential presidential candidate, and Democratic Sens. Tom Udall of New Mexico and Chris Murphy of Connecticut.

"It's impossible to know who are friends are," Paul said. His arguments put him at odds with another potential White House candidate - Republican Sen. Marco Rubio of Florida, who backed the legislation.

Meanwhile, despite recent rebel setbacks in Syria's civil war, the main opposition bloc signaled a tough line Tuesday on attending possible peace talks with Assad's regime.

Two senior members of the Syrian National Coalition said the group first wants ironclad guarantees of Assad's departure as part of any transition deal and more weapons for rebel fighters. The group's final position is to be hashed out in a three-day meeting of its General Assembly in Istanbul, Turkey, this week.

Tuesday's comments highlighted the wide gaps between many in the Syrian opposition and the regime just weeks before the United States and Russia hope to bring the sides together.