A US Senate panel has approved the use of military force in Syria, in response to an alleged chemical weapons attack.
By 10-7, the Committee on Foreign Relations moved the measure to a full Senate vote, expected next week.
The proposal allows the use of force in Syria for 60 days with the possibility to extend it for 30 days. It prevents the use of US troops on the ground.
President Barack Obama is battling to build support at home and abroad for military action.
Despite Wednesday's vote, the bill's ultimate fate in the wider Senate is unclear. And the US House of Representatives must also approve the measure.
'Credibility on the line'
So far, only 23 senators have said they support or are likely to back the resolution, according to a tally by ABC/BBC News.
Sixteen have said they oppose or are likely to oppose the resolution, while 61 votes are undecided or unknown.
However, those numbers are expected to shift as the language in the resolution changes, the White House and its congressional allies apply pressure, and lawmakers hear from their constituents.
Earlier in the day, France - whose government has strongly advocated intervention - held an extraordinary debate in the National Assembly, though MPs will not vote on the matter as the country's president can mobilise the military without their backing.
The government of Syrian President Bashar al-Assad is accused of using chemical weapons against civilians on several occasions during the 30-month conflict, most recently on a large scale in an attack on 21 August on the outskirts of Damascus.
The US has put the death toll from that incident at 1,429 - though other countries and organisations have given lower figures - and says all the evidence implicates government forces.
At a press conference on Wednesday in Stockholm, Sweden, President Obama said: "My credibility is not on the line. The international community's credibility is on the line.
"America and Congress's credibility is on the line, because we give lip-service to the notion that these international norms are important."
Mr Obama said he believed the US Congress would approve intervention, but stressed that as commander-in-chief, he had the right to act in his country's national interest regardless.
'A safer world'
The Senate foreign relations committee approved the resolution, with one abstention, after accepting an amendment by Republican Senator John McCain that advocated increasing support for rebel forces.
The measure pledges support for "decisive changes to the present military balance of power" in Syria.
It also states US policy is to "change the momentum on the battlefield in Syria so as to create favorable conditions for a negotiated settlement that ends the conflict and leads to a democratic government".
Senator Dick Durbin, a senior Democrat on the panel, said he had voted against the war in Iraq, but that "this is different".
"What we've done today is a step in the right direction," he said. "I hope it makes a safer world."
But another Democrat, Senator Tom Udall, said he had voted no because he believed it would embroil the US in the Syrian civil war.
He was joined by five Republicans in voting against the resolution, including Rand Paul and Marco Rubio, both of whom are tipped as potential 2016 presidential candidates.
Two top Obama administration officials, Secretary of State John Kerry and Defence Secretary Chuck Hagel, meanwhile continued to press the case for intervention, this time before a House of Representatives panel.
Mr Hagel said any US military strike would not be a mere "pin prick", but would reduce the Syrian government's military capability.
He said he thought there was a "very high" likelihood that Mr Assad would use chemical weapons again if the US did not act.
In Syria, Deputy Foreign Minister Faisal Mekdad said Damascus was mobilising its allies, who were "offering it all sorts of support". He cited Iran, Russia, South Africa and some Arab countries.
Syrian state TV denied reports that a former Defence Minister, General Ali Habib, had defected to Turkey.
The United Nations says more than 100,000 people have been killed and two million others have fled the country since the uprising against President Assad began in March 2011.