President Barack Obama’s plans for a military strike on Syria have won backing from key US political figures.
Barack Obama said a “limited” strike was needed to degrade President Bashar al-Assad’s capabilities in response to an alleged chemical weapons attack.
Key Republican leaders John Boehner and Eric Cantor both signaled their support for military action. Congress is expected to vote next week.
The UN earlier confirmed that more than two million Syrians were now refugees.
More than 100,000 people are thought to have died since the uprising against President Bashar al-Assad began in March 2011.
President Barack Obama and Vice-President Joe Biden met House Speaker John Boehner, House Democratic Leader Nancy Pelosi and the chairmen and ranking members from the national security committees in Washington on Tuesday.
John Boehner signaled his support for Barack Obama’s call for action, saying that only the US had the capacity to stop President Bashar al-Assad. John Boehner urged his colleagues in Congress to follow suit.
Eric Cantor, the House of Representatives majority leader, said he also backed Barack Obama.
The Virginia Republican said: “Assad’s Syria, a state sponsor of terrorism, is the epitome of a rogue state, and it has long posed a direct threat to American interests and to our partners.”
Nancy Pelosi said she did not believe Congress would reject a resolution calling for force.
Barack Obama said that Bashar al-Assad had to be held accountable for the chemical attack and that he was confident Congress would back him.
He said he was proposing military action that would degrade Bashar al-Assad’s capacity to use chemical weapons “now and in the future”.
“What we are envisioning is something limited. It is something proportional,” the president said.
“At the same time we have a broader strategy that will allow us to upgrade the capabilities of the opposition.”
Secretary of State John Kerry, Defence Secretary Chuck Hagel and the top US military officer, Gen Martin Dempsey, are appearing before the Senate Committee on Foreign Relations.
John Kerry told the panel that US allies such as Israel and Jordan were “one stiff breeze” away from potentially being hurt by any fresh chemical weapons attacks, and that US inaction would only embolden the Syrian president.
“This is not the time for armchair isolationism,” John Kerry said.
“This is not the time to be spectators to slaughter. Neither our country nor out conscience can afford the cost of silence.
“We have spoken up against unspeakable horror many times in the past. Now we must stand up and act.”
But John Kerry said again that there would be no American boots on the ground in Syria and that Barack Obama was “not asking America to go to war”.
Chuck Hagel said that “the word of the United States must mean something” and echoed John Kerry when adding: “A refusal to act would undermine the credibility of America’s other security commitments, including the president’s commitment to prevent Iran from acquiring a nuclear weapon.”
There will also be a classified briefing for all members of Congress.
Barack Obama will head to Sweden late on Tuesday for a G20 meeting sure to be dominated by Syria.
France has strongly backed the US plan for military action.
President Francois Hollande said on Tuesday: “When a chemical massacre takes place, when the world is informed of it, when the evidence is delivered, when the guilty parties are known, then there must be an answer.”
Francois Hollande called for Europe to unite on the issue, but said he would wait for the Congress vote.