Russia, as well as Syrian President Bashar al-Assad's forces and Iranian-backed fighters, were responsible for the destruction of eastern Aleppo, said German government spokesman Steffen Seibert at a government news conference.

"We know that this ruthless destruction of eastern Aleppo would not have been possible without massive military support from Russia," he said. "Russia has not prevented the crimes of the last few days although it was within its power to do so."

Seibert added that Chancellor Angela Merkel had spoken to Russian President Vladimir Putin on Tuesday and called for an immediate ceasefire.