Russia and Iran will be guilty of war crimes if they do not put pressure on Syrian President Bashar Assad to stop escalating violence in the country, says France's foreign minister.
At an emergency United Nations Security Council meeting, Jean-Marc Ayrault said Sunday was a "moment of truth" for the UN.
He said Assad's regime "has clearly made the choice of a military escalation. I am calling on Russia and Iran to pull themselves together and show responsibility, by putting a stop to this strategy. ... If not, Russia and Iran will be accomplices in war crimes committed in Aleppo."
The US, Britain, and France sought Sunday's meeting, as pro-government forces continued their intense bombardment of Aleppo. They are widely believed to be accompanied by Russian air strikes.
A monitoring group claims Syrian rebels have retaken an area in Aleppo that fell to government forces the day before, extending a punishing stalemate in the contested northern city.
The Britain-based Syrian Observatory for Human Rights, which maintains a network of local contacts, says rebels seized Handarat, a largely uninhabited Palestinian refugee camp, early Sunday.
The area is near Castello Road, a vital supply route to the city's besieged rebel-held areas. Government forces seized the Castello Road earlier this year, besieging rebel-held districts where some 250,000 people reside.
Yasser al-Yousef, a spokesman for the Nour el-Din al-Zinki rebel faction, says rebels seized Handarat late on Saturday.
The Observatory says 213 civilians have been killed by airstrikes and shelling on rebel-held areas in and around Aleppo since a ceasefire expired on Monday.