The world cannot be "silent spectators to slaughter", US secretary of state John Kerry has said as he embarks on a European visit aimed at shoring up support for military action in Syria.
But in a joint statement member states stopped short of endorsing any US-led strike, stressing "the need to move forward with addressing the Syrian crisis through the UN process".
Only France is so far committed to joining an armed response to poison gas atrocities blamed on the regime - including the August 21 attack on a Damascus suburb that America says killed at least 1,400.
He returned to Washington from a G20 summit where international divisions were laid starkly bare - with Moscow warning strikes would be illegal and blaming opposition forces for the chemical attack.
The EU ministers agreed that all the available information "seems to indicate strong evidence that the Syrian regime is responsible for these attacks".
France is the only country to have said it could join military action but President Francois Hollande has also said he will await a report by UN inspectors into the Damascus deaths before deciding. There were suggestions that their findings - which are limited to whether chemical weapons were used and not who used them - could be reported back to the UN by the end of the week.
Speaking after talks in Paris, Mr Kerry said he and Mr Obama were "exceedingly grateful" to have France alongside them and both countries knew it was no time to be "silent spectators to slaughter".
The Secretary of State is due in London on Monday for talks with Foreign Secretary William Hague in the wake of the vote by MPs against joining military action. Prime Minister David Cameron has said there was an "extremely powerful" for military action but ruled out bringing the issue back to the Commons.