Free Syrian Army fighters shout "Allahu Akbar" near Deraa in this still image taken from a video obtained by Reuters May 17, 2012. Reuters/Handout The first cell of Syrian rebels trained and armed by the CIA is making its way to the battlefield, President Barack Obama has reportedly told senators.

During a meeting at the White House, the president assured Senator John McCain that after months of delay the US was meeting its commitment to back moderate elements of the opposition.

Mr Obama said that a 50-man cell, believed to have been trained by US special forces in Jordan, was making its way across the border into Syria, according to the New York Times.

The deployment of the rebel unit seems to be the first tangible measure of support since Mr Obama announced in June that the US would begin providing the opposition with small arms.

Congressional opposition delayed the plan for several weeks and rebel commanders publicly complained the US was still doing nothing to match the Russian-made firepower of the Assad regime.

Mr McCain has been a chief critic of the White House's reluctance to become involved in Syria and has long demanded that Mr Obama provide the rebels with arms needed to overthrow the regime.

He and Senator Lindsey Graham, a fellow Republican foreign policy hawk, emerged from the Oval Office meeting on Monday cautiously optimistic that Mr Obama would step up support for the rebels.

"There seems to be emerging from this administration a pretty solid plan to upgrade the opposition," Mr Graham said.

He added that he hoped the opposition would be given "a chance to speak directly to the American people" to counter US fears that they were dominated by al-Qaeda sympathisers.

"They're not trying to replace one dictator, Assad, who has been brutal... to only have al-Qaeda run Syria," Mr Graham said.

The US announced in June, following the first allegations the Assad regime had used chemical weapons, that it would send light arms to the rebels but refused to provide anti-aircraft missiles and other heavy weapons.

American concerns were born partly out of the experience of Afghanistan in the 1980s, when CIA weapons given to the anti-Russian mujahideen were later used by the Taliban.