At least 21 civilians, including three children, were killed Thursday in Russian strikes on several rebel-held districts of Syria's Aleppo city, a monitor said.The Britain-based Syrian Observatory for Human Rights said the strikes on six neighbourhoods of the city had also injured many and the toll could rise.Turkish Prime Minister Ahmet Davutoğlu implicitly accused Russia of "war crimes" Thursday in comments at a donor conference in London, warning that the Syrian city of Aleppo was under "heavy attack" by Russian warplanes."The root cause is the war crimes committed by Syrian regime then war crimes committed by Daesh," said Davutoğlu."Those who are helping Assad regime are committing same war crimes," he said.