Moscow's suggestions that civilians were poisoned by rebel weapons on the ground have been widely rejected.
The UK's foreign secretary, a rebel commander and a weapons expert all said evidence pointed to an attack by the Syrian government, Russia's ally.
International donors have pledged $6bn (£4.8bn) in aid for Syria this year.
Seventy donor nations discussed aid efforts in the war-ravaged country in the Belgian capital, Brussels.
What happened?
