As of last month, U.S. officials warned that if any Middle Eastern nation was “even considering giving arms to the Syrian opposition,” it ought to “take a measured approach and think twice about providing arms that could have unintended consequences.”

Nonetheless, even at that time, U.S. and allied officials acknowledged that officials of Saudi Arabia and Qatar were discussing whether surface-to-air missiles might help Syrian rebels bring down Russian-made helicopters and other aircraft the Syrian army was using to move troops between trouble spots.

Following the fall of Libyan leader Muammar Gaddafi, some intelligence experts estimated that as many as 10,000-15,000 Manpads sets were looted from Libyan government stockpiles. The whereabouts of most of these are unknown.

Many U.S. officials have been wary of the notion of arming Syrian rebels with Manpads, noting that they could be easily turned on targets other than the Syrian government, including civilian airliners.

After the Soviet Union invaded Afghanistan, the CIA, with Saudi backing, provided sophisticated shoulder-fired Stinger missiles to Islamic militants seeking to oust Soviet troops.

The missiles proved deadly against Soviet helicopter gunships, but subsequently became a major headache for U.S. and western counter-terrorism agencies when anti-Soviet militants morphed into anti-Western militants.

Recent intelligence and news reporting has suggested a growing number of militants, including some affiliated with al Qaeda, have traveled to Syria to try to join anti-Assad forces. U.S. officials have said, however, that they do not believe the militants yet play a dominant role in the Syrian opposition.