Russian forces say they have briefly suspended military action in the northern Syrian city of Aleppo to allow in desperately needed humanitarian aid.
It is not clear if Syrian rebel groups will also cease fire during the daily three-hour window.
But UN officials say the window is too short to take in enough to help the large numbers of people in need.
Intense fighting has been continuing in Aleppo between rebels and Russian-backed Syrian government forces with reports of a toxic gas attack on a rebel-held area.
Medical staff said four people died and many others were injured.