A bipartisan crowd of congressional critics and overwhelming public opposition killed President Barack Obama's proposal to attack the government of Syrian President Bashar Assad last year, but in the final months of 2013, at least some members of Congress reportedly approved secret weapon transfers to Syrian rebels.

The weapons being paid for by U.S. taxpayers include anti-tank missiles and are supplied to "moderate" rebels in southern Syria via Jordan, Reuters reported Monday evening, citing unnamed U.S. and European security officials.

Some members of Congress, including leading skeptics of U.S. intervention in Syria's three-year civil war, may have been unable to know about the funding and unable to object to it.

The arms funding likely was born as a "classified annex" in the defense subcommittee of the U.S. House Committee on Appropriations, then approved by the full appropriations committee, then the full House. A similar process would have occurred in the Senate.

But members of Congress do not automatically acquire the high-level security clearance required to view classified appropriations, a staffer of the House Appropriations Committee tells U.S. News.

Members of Congress without sufficiently high levels of clearance lose their right to know anything about classified appropriations – including dollar amounts and funding recipients – and therefore cannot participate in the approval process.

The committee staffer was unable to provide additional information about the reported funds for Syrian rebels.

Spokespeople for several congressmen who opposed intervention in Syria tell U.S. News they are looking into the issue. One leading intervention opponent has not seen the classified annex allocating funds to the rebels, according to a spokeswoman.

Officials cited by Reuters said several months of future arms deliveries are already funded by Congress. An American official told Reuters supportive members of Congress and national security officials are confident the weapons won't be taken by powerful al-Qaida-associated rebel groups who have attacked secular rebels and horrified Western media audiences by performing grisly public executions.

U.S. support for Syrian rebels – at least publicly acknowledged support – previously appeared to be tapering off. Defense Secretary Chuck Hagel said Dec. 12 the U.S. would cease providing non-lethal aid to rebels – after incurring $260 million in such expenses – citing "how complicated and dangerous this situation is and how unpredictable it is."

Many facts about the ongoing arms mission and its legislative history are unknown. It's possible the funding was attached to the 2014 National Defense Authorization Act signed by Obama on Dec. 26.

Polls suggest that Americans are reluctant to support any intervention in Syria.

A Pew Research Center poll conducted June 12-16 found 70 percent of Americans oppose providing arms to rebels and that 60 percent believe the rebels may be no better than the Assad regime. A survey conducted June 28-July 8 by Quinnipiac University found 61 percent of Americans believe it's not in the country's national interest to intervene in the war and that 59 percent oppose arming Syrian rebels.

An apparent chemical weapons attack on the suburbs of Damascus Aug. 21 led Obama to announce his intention to conduct air strikes against Assad's government. Obama decided to seek congressional approval Aug. 31 after mounting public opposition. Rep. Alan Grayson, D-Fla., accused administration officials of providing members of Congress misleading intelligence in closed-door sessions to convince them to favor war.

The drumbeat for intervention wilted when it became clear the administration lacked the votes in Congress to win authorization. A flurry of polling confirmed skepticism not just of the proposed strikes, but also opposition to arming rebels. A Washington Post/ABC News poll conducted Aug. 28-Sept. 1 found 59 percent opposed air strikes on Syria and that 70 percent opposed arming the rebels. A CNN poll conducted Sept. 6-8 found 69 percent of Americans believed it was not in America's interest to intervene in the civil war.

Classified annex provisions occasionally enrage members of Congress who are unaware of their content until they become law. Sen. John McCain, R-Ariz., was infuriated earlier this month when a classified annex included in a $1.1 trillion spending package forbade the CIA from transferring its drone program to the Department of Defense. Senate Majority Whip Dick Durbin, D-Ill., explained to Roll Call that all members do not have access to all annex material.