Leaders of the U.S. Senate foreign relations committee say they have reached an agreement on a draft authorization for the use of military force in Syria.
The resolution would bar American ground troops for combat operations and set a deadline for any action.
The measure would set a time limit of 60 days and says the president could extend that for an additional 30 days unless Congress has a vote of disapproval.
Democratic Senator Bob Menendez of New Jersey, chairman of the committee, and Senator Bob Corker of Tennessee, the top Republican, agreed on the measure late Tuesday. The foreign relations committee will vote on the draft resolution Wednesday.
The draft came after an afternoon hearing in Washington. Secretary of State John Kerry, Defence Secretary Chuck Hagel, and Joint Chiefs Chairman Gen. Martin Dempsey were dispatched to the Senate to help persuade lawmakers to support a resolution authorizing limited military strikes against Syria.
Kerry said the number of chemical weapons attacks by Syrian government forces is in the double digits and that rebels put the number even higher.
The figure cited by Kerry is significantly higher than any previous public estimate from the U.S. Before last month's suspected chemical attack in the Damascus suburbs, U.S. officials had spoken of several earlier incidents. But no one had put the total in double figures.
Kerry told members of the Senate foreign relations committee that Syrian President Bashar al-Assad's regime would definitely use chemical weapons again unless the U.S. takes military action.
- Read Brian Stewart on the lack of options and many 'known unknowns' in Syria
- Syria's Assad warns foreign strikes would have repercussions
- See the limited options the U.S. has for a strike
Kerry said the debate about military strikes is not about President Barack Obama's "red line," but the world's.
"This is not the time for armchair isolationism. This is not the time to be spectators to slaughter," he said.
Kerry made one thing very clear: There will be no American boots on the ground.
He said there was no problem in having language in legislation that "has zero capacity for American troops on the ground."
Some lawmakers have expressed reluctance about being drawn into a larger conflict. But Kerry stressed that what Obama is seeking would be military action limited in scope and duration that would send a message to the Assad regime that it can't get away with using chemical weapons.
Obama approved lethal aid to Syrian rebels
Hagel acknowledged that Obama approved plans in June to give lethal aid to Syrian rebels, making the decision public for the first time.
The UN refugee agency reported Tuesday the number of refugees fleeing Syria's violence has surpassed the two million mark.
Antonio Guterres, the head of the Office for the UN High Commissioner for Refugees, said Syria is hemorrhaging an average of almost 5,000 citizens a day across its borders, many of them with little more than the clothes they are wearing. Nearly 1.8 million of the refugees have fled in the past 12 months alone, he said. Another four million have been displaced within Syria's borders.
"Syria has become the great tragedy of this century — a disgraceful humanitarian calamity with suffering and displacement unparalleled in recent history," he said.
Hagel and Corker, the top Republican on the Senate foreign relations committee, both referred to the covert aid. Corker said he has been dismayed at the lack of support that has flowed to the rebels despite the promises of lethal aid.
Hagel told the Senate committee that the Pentagon has not been directly involved because it is "a covert action." Officials have spoken quietly about the expected CIA aid but say none has been delivered.
Hagel also said that several key allies in the region strongly support U.S. military action in Syria.
He said that France, Turkey, Saudi Arabia and the United Arab Emirates and others in the region are key partners in any U.S. action. He added that U.S. forces were ready to act whenever Obama gives the order.
Earlier, Obama's call for a military strike won significant momentum on Tuesday, with leaders of both parties in Congress announcing they are convinced that Assad used chemical weapons against his own people and that the U.S. should respond.
- Read Nahlah Ayed on how Syria is ready for U.S. attack, having expected one for years
- Syria's digital war explodes on social media fronts
- Is an attack on Syria legal?
Republican House Speaker John Boehner emerged from a White House meeting and told reporters: "This is something that the United States, as a country, needs to do. I'm going to support the president's call for action. I believe that my colleagues should support this call for action."
House majority leader Eric Cantor and House Democratic leader Nancy Pelosi also said they will support Obama because the U.S. has a compelling national security interest to prevent the use of weapons of mass destruction.
Obama remains confident
Obama met with more than a dozen lawmakers in the White House to press the case for strikes aimed at dismantling Assad's chemical weapons capabilities. The president said he's confident Congress will authorize the strike and tried to assure the public that involvement in Syria will be a "limited, proportional step."
"This is not Iraq, and this is not Afghanistan," Obama said.
Obama indicated he is open to changing the language to address lawmakers' concerns and called for a prompt vote.
"So long as we are accomplishing what needs to be accomplished, which is to send a clear message to Assad, to degrade his capabilities to use chemical weapons, not just now but also in the future, as long as the authorization allows us to do that, I'm confident that we're going to be able to come up with something that hits that mark," Obama said.
After Obama met with the congressional leadership, administration officials offered a classified briefing for all members of Congress.
The U.S. said it has proof that the Assad regime is behind attacks that Washington claims killed at least 1,429 people, including more than 400 children. The Britain-based Syrian Observatory for Human Rights, which collects information from a network of anti-regime activists, says it has so far only been able to confirm 502 dead.
Boehner said only the United States has the capability and the capacity to stop Assad.
"We have enemies around the world that need to understand that we're not going to tolerate this type of behaviour. We also have allies around the world and allies in the region who also need to know that America will be there and stand up when it's necessary," he said.