President Barack Obama has agreed to discuss Russia's proposal that Syria hand over chemical weapons, the White House said Tuesday after Damascus confirmed it would accept such a deal.

The United Nations Security Council planned to meet behind closed doors at 4 p.m., even as Obama prepared to address Congress and the American people to make the case for authorization to use military strikes if diplomatic solutions fail.

British Prime Minister David Cameron said the U.S., France and Britain would propose a Security Council resolution.

Earlier, Syria Foreign Minister Walid al-Moualem told NBC News in Moscow that he hoped acceptance of the peaceful solution would put an end to the war.

The building momentum behind Russia's plan, which had already been endorsed by China and Iran, came only 24 hours after Secretary of State John Kerry raised a weapons handover at a news conference in London.

Obama said Monday that the Russia plan offered a potential path that averted U.S. military strikes, but Kerry cautioned that the only reason the Russia solution has potential legs at all is because of a credible threat of force.

U.S. Secretary of State John Kerry testifies before the House Armed Services Committee Tuesday, saying that the Obama administration will not wait for very long on a possible Syrian chemical weapons proposal.

Nothing focuses the mind like the prospect of a hanging, Kerry told a congressional committee Tuesday. He said Obama would look at the plan but added: We re waiting for that proposal, but we re not waiting for long.

Kerry said it had been the credible use of force by the U.S. that has for the first time brought this regime to even acknowledge that they have a chemical weapons arsenal, adding that the threat of military action is more compelling if the Congress stands with the commander in chief.

Secretary of Defense Chuck Hagel echoed that line to the committee, saying the Russia deal could be a real solution to this crisis, but added: We must be clear-eyed and ensure it is not a stalling tactic by Syria and its Russian patrons.

But Russian President Vladimir Putin said later Tuesday that the proposal can work only if the United Sates and its allies reject the use of force.

Senior senators - including John McCain, R-Ariz., and Chuck Schumer, D-N.Y. - announced they were working on a new plan that would authorize the president to use force only if Syria did not comply with a U.N. resolution to remove chemical weapons by a pre-determined deadline.

Senate Minority Leader Mitch McConnell announces Tuesday that he will not be voting in favor of a resolution to use U.S. military force in Syria.

Even as they discussed their move, Senate Republican leader Mitch McConnell announced his opposition to military strikes against Syria. And Sen. Edward Markey, D-Mass., a member of the Foreign Relations Committee and Kerry's successor in the Senate, said he would not support the use of force resolution passed by the committee, calling it too broad.

The president traveled to Capitol Hill shortly after noon Tuesday to meet with the Senate Democratic Caucus and Senate Republican Conference before delivering an address to the nation from the East Room of the White House at 9:01 p.m. ET. Kerry said that despite a Senate delay on a vote after the Russians made their proposal, nothing has changed on the administration request for congressional action, though he said the president may talk to congressional leaders about timing of a vote. In a further development, a spokesman for Vladimir Putin said the Russian president had discussed the weapons handover plan with Obama at last week s G-20 summit. That shed a different light on Kerry s mention of the plan at a news conference in London on Monday. That had previously been characterized by spokesman Jen Psaki as an off-the-cuff rhetorical argument. Obama's case for limited airstrikes targeting Assad's regime was boosted early Tuesday when a Human Rights Watch report blamed Syrian government forces for the Aug. 21 poison gas attack that killed hundreds of people. Advertise | AdChoices The U.S.-based rights group said it had reached its conclusion after analyzing witness accounts, remnants of the weapons used and medical records of victims. HRW said it did not believe the attack could have been carried out by rebels or other terrorists as a smokescreen, as suggested by Assad. Human Rights Watch and arms experts monitoring the use of weaponry in Syria have not documented Syrian opposition forces to be in possession of the 140mm and 330mm rockets used in the attack, or their associated launchers, the report added. Russia s diplomatic solution appeared to be gathering momentum internationally -- as an attractive option for many U.S. allies who agree with the White House stance against chemical weapons but who are reluctant to be drawn into another Middle East military conflict. Sen. John McCain, R-Ariz., and Sen. Chuck Schumer, D-N.Y., are working with other senators on an alternative resolution to dealing with Syria and its chemical weapons. NBC News' Kasie Hunt reports. Russian Foreign Minister Sergei Lavrov explained his proposal during a pre-planned 14-minute phone call to John Kerry as the U.S. secretary of state flew from London to Washington Monday. U.S. officials said Kerry expressed concern that it would be hard to verify whether Syria had complied with any such plan, or to know if the regime had still kept some of its chemical weapons stockpiles. Adding to international concern, Turkey s state-run Anadolu agency reported that Syrian jets bombed the border town of Tel Abyad on Monday, prompting yet more Syrians to seek refuge in Turkey. Thousands had already flooded across the border, leaving authorities struggling to cope. NBC News' Courtney Kube, Kasie Hunt, Andrea Mitchell, Andy Eckardt and Kelly O'Donnell contributed to this report, along with The Associated Press and Reuters.

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