Kerry says support for action against Syria is growing
US Secretary of State John Kerry has said the number of states ready to take military action against Syria's government is in the "double digits".
Speaking in Paris, he said the world could not be "silent spectators to slaughter" after Syria's alleged use of chemical weapons against its civilians.
The US accuses President Bashar al-Assad's forces of killing 1,429 people in a gas attack on 21 August.
EU foreign ministers say there should be no action before a UN report.
French President Francois Hollande, a key ally for the US on military action against Mr Assad, has said he expects the preliminary UN report into the incident to be submitted at the end of next week.
A G20 summit in Russia failed to produce international agreement on military action, with US President Barack Obama at odds with Russia's President Vladimir Putin, who blames the gas attack on rebels.
Mr Obama has said any military action will be "limited both in time and scope - designed to deter the Syrian government from gassing its own people again and degrade its ability to do so".
Syria's chemical weapons
- The CIA believes Syria has had a chemical weapons programme "for years and already has a stockpile of CW agents which can be delivered by aircraft, ballistic missile, and artillery rockets"
- Syria is believed to possess mustard gas and sarin, a highly toxic nerve agent
- The CIA also believes that Syria has attempted to develop more toxic and more persistent nerve agents, such as VX gas
- A report citing Turkish, Arab and Western intelligence agencies put Syria's stockpile at approximately 1,000 tonnes of chemical weapons, stored in 50 towns and cities
- Syria has not signed the Chemical Weapons Convention (CWC) or ratified the Biological and Toxin Weapons Convention (BTWC)
Sources: CSIS, RUSI
Some 100,000 people have been killed in the two-and-a-half-year-old Syrian conflict, according to the UN.'Munich moment'
Mr Kerry, who is in Europe for a four-day visit, met his French counterpart Laurent Fabius in Paris, where both men spoke of their determination to respond to the use of chemical weapons in Syria.
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.
"This is the time to pursue a targeted and limited but clear and effective response that holds dictators like Bashar Assad responsible for the atrocities which they commit."
"There are a number of countries, in the double digits, who are prepared to take military action," Mr Kerry said.
This was more countries than could actually be used "in the kind of military action being contemplated", he added.
Earlier, in the Lithuanian capital Vilnius, Mr Kerry welcomed a statement on Syria by EU foreign ministers who were meeting there.
The EU ministers said available intelligence "seems to indicate strong evidence that the Syrian regime is responsible for the attack" and urged a "clear and strong response".
But they added that they welcomed French President Francois Hollande's call to wait for the report before taking any further action.
Mr Kerry is due to meet Arab League representatives in Paris before travelling to London for further talks with UK Foreign Secretary William Hague.'Defeat for humanity'
Both Russia and China, which have refused to agree to a UN Security Council resolution against Syria, insist any military action without the UN would be illegal.
President Obama faces a tough week of trying to persuade Congress to authorise military action.
He has only a few days to convince Congress, which returns from its summer recess on Monday. Both the Senate and House of Representatives could vote on the Syrian issue next week.
A poll commissioned by the BBC and ABC News suggested more than a third of Congress members were undecided whether or not to back military action - and a majority of those who had made a decision said they would vote against the president.
Many remain concerned that military action could draw the US into a prolonged war and spark broader hostilities in the region.
At the Vatican, Pope Francis called for "reconciliation and peace" in Syria. "War always marks the failure of peace, it is always a defeat for humanity," he told Roman Catholics at a mass peace vigil on St Peter's Square.
Vigils were also held in churches, mosques and synagogues around the world.
Small crowds of demonstrators rallied in New York's Times Square and near the Capitol in Washington on Saturday to oppose any attack on Syria, the Associated Press news agency reports.