US Secretary of State John Kerry is meeting Arab League leaders in Paris as part of a European tour to gather support for intervention in Syria, reports BBC News.
Earlier Mr Kerry said the number of nations prepared to take military action was now in "double digits", but the list has not been made public.
France strongly supports intervention in response to the use of chemical weapons in Damascus last month.
But it wants to wait for a report by UN weapons experts before taking action.
From Paris, Mr Kerry will travel to London where he will meet the Palestinian president Mahmoud Abbas and British Foreign Secretary William Hague.
Meanwhile, inside Syria, there are reports that rebel forces have taken control of the historic Christian town of Maalula, north of Damascus.
Abdel Rahman, the director of the Syrian Observatory for Human Rights, a UK-based activist group, told the AFP news agency that troops loyal to Syrian President Bashar al-Assad had withdrawn form the area.
During a news conference with his French counterpart Laurent Fabius on Saturday, Mr Kerry said the world could not be "silent spectators to slaughter" after Syria's alleged use of chemical weapons against its civilians.
The US accuses Mr Assad's forces of killing 1,429 people in a sarin gas attack on 21 August.
Repeating a phrase he used earlier in the week, Mr Kerry said the international community was facing a "Munich moment" - a reference to the policy of appeasement that failed to stop Nazi Germany in the 1930s.
"We in the United States know, and our French partners know, that this is not the time to be silent spectators to slaughter," he said.
He insisted there was growing support for Washington's call for intervention in Syria, saying: "There are a number of countries, in the double digits, who are prepared to take military action."
This was more countries than could actually be used "in the kind of military action being contemplated", Mr Kerry added.
Mr Fabius - who staunchly backs Mr Kerry on this issue - added that there was "wide and growing support" for action.
Earlier on Saturday, in the Lithuanian capital Vilnius, Mr Kerry welcomed a statement on Syria by EU foreign ministers who were meeting there.
The EU ministers urged a "clear and strong response" to the alleged chemical attack.
But the EU also welcomed French President François Hollande's call to wait for the UN weapons inspectors' report before taking any further action.
Mr Hollande said he expected the report to be ready by next weekend.
Meanwhile the BBC has learnt that the UK government has sent chemical protection suits to some members of the opposition forces in Syria this week, as it continues to give technical and non-lethal aid to members of the Syrian national coalition.
Read more of this report from BBC News.