"Tomorrow will be a moment of truth, a moment of truth for all the members of the Security Council," Ayrault said, standing by his US colleague Secretary of State John Kerry.
"Do you want a ceasefire in Aleppo, yes or no? And the question is in particular for our Russian partner."
France has drafted a resolution for the Security Council demanding a ceasefire in Syria and an end to Russia and the regime's bombardment of rebel-held eastern Aleppo.
Russia, as a permanent member of the council, wields a veto and Ayrault admitted that there was work to do on the resolution and it was far from clear whether Moscow would accept it.