WASHINGTON (AP) -- A Senate panel voted on Tuesday to provide weapons to rebels battling the forces of Syrian President Bashar Assad, the first time lawmakers have endorsed the aggressive U.S. military step of arming the opposition in the 2-year-old civil war.

With a degree of trepidation, the Foreign Relations Committee voted 15-3 for a bill that would provide lethal assistance and military training to vetted rebel groups, and would slap sanctions on anyone who sells oil or transfers arms to the Assad regime such as Iran and Russia. The measure also establishes a $250 million fund to aid in the transition if and when Assad falls.

An intense committee debate over the bill underscored congressional fears about greater U.S. military 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 fate of the bill is uncertain, with opposition among several senators and far less enthusiasm in the House for stepped-up U.S. military action. The legislation does send a strong message as the Obama administration mulls its next step.

After some 90 minutes of discussion - and rejection of several amendments to undercut the measure, a bipartisan argument for increased U.S. action in Syria swayed lawmakers.

"The greatest humanitarian crisis in the world is unfolding in and around Syria," said Sen. Bob Menendez, D-N.J., the committee chairman. "Vital U.S. interests are at stake including the stability of the Middle East, loose chemical weapons, and the danger that Syria becomes a safe haven for extremists. 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. "This bill lays out a strategy."

The United Nations estimates that more than 70,000 people have been killed and more than 1 million displaced after two years of fighting between Assad forces and rebels. The Obama administration has provided millions of dollars in humanitarian assistance but has been wary of calls to arm the rebels or launch military strikes despite recent evidence that Assad has used chemical weapons on his people.

The administration is mulling its next step as Secretary of State John Kerry pursues a diplomatic solution.

Opposing the legislation were Sens. Rand Paul, R-Ky., a potential presidential candidate in 2016, and Democratic Sens. Tom Udall of New Mexico and Chris Murphy of Connecticut.

Udall questioned whether the United States would know what rebel groups it was arming as it introduced more lethal weapons into a chaotic situation while Murphy argued that the U.S. hasn't learned from history.

"We have failed over and over again in our attempts to pull the strings of Middle Eastern politics," he said.

Paul said the U.S. is war weary and reluctant to get involved in a murky conflict with so many factions. He said there is no assurance that the weapons would end up in the hands of "liberty-loving, Jeffersonian-type of democrats."

"It's impossible to know who are friends are," he said.

His arguments put him at odds with another potential White House candidate - Republican Sen. Marco Rubio of Florida, who backed the legislation and insisted that it was critical to help groups battling the well-armed, pro-Assad forces and radical jihadists.

The committee turned back two amendments sponsored by Paul, one saying the 2001 Authorization for the Use of Military Force does not allow intervention in Syria and another that barred weapons to Syria.

Paul pointed out the irony that one of the most effective rebel groups fighting Assad is Jabhat al-Nusra, an al-Qaida-affiliated group. The goal of the legislation is to ensure that the rebel groups meet a certain criteria with no links to terrorism.

The panel also rejected a Udall amendment that would have limited the weapons to .50-caliber arms and smaller. The senator warned that heavier weapons could end up in the hands of U.S. enemies.

Sen. John McCain, R-Ariz., a fierce proponent of aggressive U.S. military might against Syria, pointed out that Assad's forces have used helicopter gunships, tanks, Scud missiles and heavy artillery.

"The senator wants to use shotguns against Scud missiles," McCain said derisively.

Udall said Saudi Arabia and Qatar are providing weapons to the opposition forces. The United States, he said, "could turn over the weapons we're talking about and next day they end up in the hands of al-Qaida."

On Wednesday, Kerry will meet with 10 of America's closest Arab and European allies in Jordan. Officials said the gathering has two aims: to change Assad's calculation, only fortified by his recent military successes, that he can win the war militarily, and to persuade both the government and the opposition to attend peace talks next month in Geneva.

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Associated Press writer Bradley Klapper in Muscat, Oman, contributed to this report.