US President Barack Obama cleared the first hurdle Wednesday in his race to win domestic congressional backing for strikes to punish Syria's alleged use of chemical weapons.

Bashar al-Assad's defiant regime vowed to retaliate against any US action, but the White House won the support of a key Senate panel for its plan for a limited military response.

Secretary of State John Kerry also said that Washington had recruited other nations to its cause, promising that allies in the region would support American and French strikes.

The US Congress could vote as early as next week to authorise action, but the threat has done nothing to calm the chaos on the ground, and refugees continue to fleeSyria.

The UN refugee agency and four states which have taken in hundreds of thousands issued a plea for the international community to end the "cycle of horror."

As Obama's big hitters lobbied Congress in Washington, the president used an appearance during a visit to Sweden to rally global support -- and to deny he is isolated.

"I didn't set a red line. The world set a red line," Obama said, referring to international rules banning the use of chemical weapons, even in wartime.

"My credibility is not on the line," Obama said. "The international community's credibility is on the line and America and Congress' credibility is on the line."

Obama was to travel on to the G20 summit in Saint Petersburg, Russia, where he is expected to continue seeking international support for strikes against Syrian regime targets.

The Syrian civil war has raged for two-and-a-half years and more than 100,000 have died as Assad's forces battle a popular uprising that evolved into an armed insurgency.

Obama, who won office on a promise to extricate US forces from wars in the Muslim world, resisted military involvement until last month's alleged poison gas attack

According to US intelligence, more than 1,400 people living in rebel-held suburbs of Damascus were killed in the strike, which involved the use of the sarin nerve gas.

Other bodies have given lower estimates of the death toll but there is broad consensus in Western and Arab capitals that the attack took place and that government forces were to blame.

Obama argues that the use of chemical weapons breaks a taboo -- a global "norm" of warfare -- and constitutes both a crime under international law and a threat to US security.

He has asked the US Congress to authorize a limited military response, which American officials say will be limited to cruise missile strikes, and on Wednesday that goal came nearer.

After hearing from Kerry and Defense Secretary Chuck Hagel, the Senate Foreign Relations Committee approved a resolution that would authorize US military intervention.

The vote was not unanimous, however, and the panel's amendments imposed a a 90-day deadline on action and explicitly barred the prospect of American boots on the ground.

Senate leaders said the full chamber will vote next week on the motion, and Obama is expected to carry the day -- his Democratic supporters hold a majority in the Senate.

In the House of Representatives, however, where Obama's Republican opponents hold a majority, a tougher vote is expected. It will begin its consideration next week.

Both parties are divided, with isolationists and libertarians joining anti-war liberals in opposing intervention and neoconservative hawks urging Obama to go further.

Nevertheless, White House officials signalled confidence that they would carry the day, and Kerry said an international coalition was gathering behind the attack plan.

"We are building support with ... other countries, among them the Arab League," he said, adding that some Arab states had even offered to cover the cost of the operation.

"Specific countries that have talked in terms of acting" were "Saudi Arabia, the Emirates, Qataris, the Turks and the French."

Washington is also weighing greater support for Syrian rebels by having the Pentagon take charge of arming the opposition instead of a clandestine effort by the CIA, officials said.

White House officials have said that at the G20 Obama will meet French President Francois Hollande, the main foreign backer of a strike, as well as the leaders of China and Japan.

No bilateral meeting is planned with Russian President Vladimir Putin, a strong Assad supporter, but the White House suggested there would likely be some kind of dialogue.

Syrian Deputy Foreign Minister Faisal Muqdad, meanwhile, told AFP in an interview that Damascus "has taken every measure to retaliate against... an aggression."

"The Syrian government will not change position even if there is World War III," he said.

Both Russia and Iran, another close Syrian ally, have warned that a military intervention would have devastating regional consequences.

In an interview broadcast Wednesday, Putin did not exclude strikes if it were proven the regime had carried out the gas attack and the UN Security Council approved.

Yet Muqdad insisted Moscow had not wavered in its support of Damascus.

"The Russian position is unchanged; it's a responsible position of a friend that is in favour of peace," he said.

In Paris, French Prime Minister Jean-Marc Ayrault urged lawmakers to back military action in response to "the most massive and terrifying use" of chemical weapons this century.

The session was fiery, but no vote was expected as French President Francois Hollande does not need parliamentary approval to launch military action.

In Geneva, Antonio Guterres, the UN High Commissioner for Refugees, held talks with ministers from Syria's neighbours Lebanon, Jordan, Turkey and Iraq.

"A political solution to end this cycle of horror is urgently needed," he said.

The four countries have received the overwhelming majority of the two million Syrians who have fled their homeland.