A diplomatic solution to the fighting looked unlikely as U.S. and Russian diplomats disagreed at a U.N. Security Council meeting called to discuss the violence, which has escalated since a ceasefire collapsed last week.
Rebels, who are battling President Bashar al-Assad's forces for control of Aleppo, said any peace process would be futile unless the "scorched earth bombing" stopped immediately.
Capturing the rebel-held half of Syria's largest city, where more than 250,000 civilians are trapped, would be the biggest victory of the civil war for Assad's forces.
They have achieved their strongest position in years thanks to Russian and Iranian support and launched a fresh offensive for a decisive battlefield victory on September 22. Residents and rebels say thousands have been killed in the new strikes.
"What Russia is sponsoring and doing is not counter terrorism, it is barbarism," U.S. Ambassador to the United Nations, Samantha Power, told the 15-member council.
"Instead of pursuing peace, Russia and Assad make war. Instead of helping get lifesaving aid to civilians, Russia and Assad are bombing the humanitarian convoys, hospitals, and first responders who are trying desperately to keep people alive."
The French and British foreign ministers also took aim at Russia, saying it could be guilty of war crimes.
But Russia defended its position.
"In Syria hundreds of armed groups are being armed, the territory of the country is being bombed indiscriminately and bringing a peace is almost an impossible task now because of this," Russian U.N. Ambassador Vitaly Churkin told the council.
