US President Barack Obama is weighing "limited and narrow" action against Syria as the administration bluntly accused Bashar Assad's government of launching a chemical weapons attack that killed at least 1,429 people - far more than previous estimates - including more than 400 children.
With France as his only major ally, Mr Obama told reporters he has a strong preference for multilateral action but "we don't want the world to be paralysed".
It came as UN personnel carried out a fourth day of inspection in a bid to determine precisely what happened in the attack last week. The international contingent arranged to depart Syria on Saturday and head to laboratories in Europe with the samples they have collected.
Mr Obama met with his national security aides at the White House and then with diplomats from Baltic countries, saying he has not yet made a final decision on a response to the attack.
But the administration did nothing to discourage the predictions that he would - and soon. It was an impression heightened both by strongly worded remarks by Secretary of State John Kerry's remarks and the release of an unclassified intelligence assessment that cited "high confidence" that the Syrian government carried out the attack.
In addition to the dead, the assessment reported that about 3,600 patients "displaying symptoms consistent with nerve agent exposure" were seen at Damascus-area hospitals after the attack.
To that, Mr Kerry added that "a senior regime official who knew about the attack confirmed that chemical weapons were used by the regime, reviewed the impact and actually was afraid they would be discovered." He added for emphasis: "We know this."
The assessment did not explain its unexpectedly large casualty count, far in excess of an estimate from Doctors without Borders. The Assad government has accused rebels of carrying out the attacks.
The looming confrontation is the latest outgrowth of a civil war in which Assad has tenaciously - and brutally - clung to power. An estimated 100,000 civilians have been killed in more than two years, many of them as a result of attacks by the Syrian government on its own citizens.