Despite major powers agreeing to a pause in combat in Syria, Russia has pressed on with relentless bombing in support of President Bashar al-Assad.
The "cessation of hostilities" agreement does not take effect for a week, at a time when Assad's government is poised to win its biggest victory of the war with the backing of Russian air power.
The deal would allow humanitarian aid to reach besieged towns, but several Western countries said there was no hope for progress without a halt to the Russian bombing. The Kremlin has suggested it might not stop its air strikes, even when the cessation of hostilities takes effect.
The conflict in Syria has killed at least 250,000 people, made 11 million homeless and sent hundreds of thousands fleeing into Europe.