US President Barack Obama has said its too early to say if a Russian plan to secure Syria's chemical weapons can stop US air strikes.
But he has promised to give diplomacy a chance.
In a national address, he said that for reasons of moral decency, they cannot look away after innocent children were gassed to death in an attack he blames on President Bashar al-Assad's regime.
"The images from this massacre are sickening: Men, women, children lying in rows, killed by poison gas," Obama said in the 16-minute speech.
Obama said he will keep the US Navy on station off the Syrian coast to keep up the pressure on Assad's regime while the diplomatic track evolves.
That warning, delivered in stern tones, may also have been meant as a sign to Russia that he will not stand for delaying tactics or endless diplomacy, which critics say is the inevitable result of Moscow's initiative.
The president is to dispatch Secretary of State John Kerry to Geneva to meet his Russian counterpart for talks on the crisis on Thursday.
And he pledged to also work personally with Russian President Vladimir Putin, with whom he has a frosty relationship as US-Russia ties plumb their worst depths since the Cold War.
Obama said he understood after the wars in Afghanistan and Iraq that Americans were weary of costly conflicts abroad -- and said he was more interested in ending wars than beginning new ones.
But he said that if America did not act, chemical weapons would be used again in flagrant violations of international law.
And he made this appeal:
