Free Syrian Army fighters take up positions with their weapons behind a wall in Aleppo's Sheikh Saeed neighbourhood September 9, 2013. REUTERS/Nour Kelze

By Stephen Kalin and Arshad Mohammed

BEIRUT/LONDON (Reuters) - As President Barack Obama struggled to rally Congress and the American people behind military action in Syria, Russia seized on a remark by his secretary of state on Monday to say Damascus should save itself by handing over its chemical weapons.

John Kerry was quick to dismiss as hypothetical his own comment that Syrian President Bashar al-Assad could avert U.S. strikes by surrendering his chemical arsenal to international control. But Assad's ally Russia quickly turned it into a firm proposal that was "welcomed" by Damascus and echoed by U.N. chief Ban Ki-moon.

Rebels fighting Assad's forces on the ground, where hundreds are being killed by conventional bullets and explosives every week, dismissed any such weapons transfer as impossible to police and a decoy to frustrate U.S. plans to attack.

The White House said it was "seriously skeptical" but would take a "hard look" at the proposal.

Kerry later called Lavrov to tell him that while his remarks had been rhetorical and the United States was not going to "play games," if there was a serious proposal, then Washington would take a look at it, a senior U.S. official said.

With President Obama preparing to make his case in television interviews later on Monday to Americans wary of involvement in another distant war, the armaments proposal could complicate his task - or give the president an alternative to military action.

The outcome of votes in Congress remains hard to predict.

Obama has argued that Assad, fighting to continue his family's four-decade rule in a civil war well into its third year, must be punished for what Washington says was a poison gas attack on rebel areas that killed over 1,400 people on August 21.

The president surprised friends and foes by turning to Congress for approval, delaying any U.S. response.

Asked by a reporter during a visit to London whether there was anything Assad's government could do or offer to stop a U.S. military strike, Secretary of State Kerry answered:

"Sure. He could turn over every single bit of his chemical weapons to the international community in the next week - turn it over, all of it without delay and allow the full and total accounting. But he isn't about to do it and it can't be done."

The State Department later said Kerry had been making a rhetorical argument about the impossibility of Assad turning over chemical weapons, which Assad denies his forces used.

RUSSIAN PROPOSAL

Less than five hours later, Russian Foreign Minister Sergei Lavrov said he had put what sounded like Kerry's proposal to his visiting Syrian counterpart during talks in Moscow. Walid al-Moualem said Damascus welcomed the Russian initiative - while not spelling out whether Syria would, or even could, comply.

Russian President Vladimir Putin has blocked U.N. action against Assad and says Obama would be guilty of unlawful aggression if he launches an attack without U.N. approval.

Lavrov said: "If the establishment of international control over chemical weapons ... makes it possible to avoid strikes, then we will immediately get to work with Damascus."

Lavrov said Russia was also urging Syria to eventually destroy the weapons and become a full member of the Organisation for the Prohibition of Chemical Weapons (OPCW).

Shortly afterward, United Nations Secretary General Ban took up the same theme, saying that he might ask the Security Council to end its "embarrassing paralysis" over Syria and agree to act.

Asked about Lavrov's proposal, Ban said: "I'm considering urging the Security Council to demand the immediate transfer of Syria's chemical weapons and chemical precursor stocks to places inside Syria where they can be safely stored and destroyed."

Ban has said that any action that lacks the approval of the world security body could worsen the situation in Syria.

U.N. chemical weapons inspectors were in Damascus at the time of the mass poisoning, which Assad and Putin have blamed on rebel forces. Ban said that if the evidence they were able to gather - after lengthy bargaining over their movements with Syrian officials - proved the use of toxins, the world must act.

Syria, which has never signed a global treaty banning the storage of chemical weapons, is believed to have large stocks of sarin, mustard gas and VX nerve agents - the actual use of which is banned by a 1925 treaty to which Damascus is a signatory.

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