Defense Secretary Leon Panetta on Thursday acknowledged for the first time that the Pentagon had backed proposals to arm the Syrian opposition battling to oust President Bashar al-Assad.

The idea -- ultimately rejected -- was first floated by then-secretary of state Hillary Clinton, who met privately with David Petraeus, CIA chief at the time, in the summer of 2012 as fighting raged in Syria.

They proposed vetting rebel groups and training fighters in a plan which they presented to the White House, according to the New York Times, quoting administration officials.

But the administration of President Barack Obama was worried about the risks of pouring more arms into the volatile conflict and rejected the idea, sticking instead to providing humanitarian assistance and non-lethal aid.

Panetta and the chairman of the Joint Chiefs of Staff, Martin Dempsey, admitted under questioning in the Senate Armed Services Committee Thursday that they had both supported the idea.

"I would ask again, both of you, what I asked you last March when 7,500 citizens of Syria had been killed. It's now up to 60,000. How many more have to die before you recommend military action?" Senator John McCain asked them.

"And did you support the recommendation by then secretary of state Clinton and then head of CIA General Petraeus that we provide weapons to the resistance in Syria? Did you support that?"

"We did," replied Panetta. "We did," added Dempsey.

McCain, who has long advocated arming the rebels, said in a statement later he "was very pleased to hear" both men say they supported the proposal.

"What this means is that the president overruled the senior leaders of his own national security team, who were in unanimous agreement that America needs to take greater action to change the military balance of power in Syria," he said.

McCain called on Obama to heed the advice of his former and current national security leaders and "immediately take the necessary steps, along with our friends and allies, that could hasten the end of the conflict in Syria."

"The time to act is long overdue, but it is not too late."