UN Chief Ban Ki-moon has said he was appalled by the chilling military escalation in Syria’s battleground city of Aleppo where residents cowered indoors as air strikes toppled buildings and killed at least 45 civilians. The Security Council was set to meet Sunday to discuss the upsurge in violence since the Syrian army announced an offensive to retake the rebel-held east of the devastated city. The UN said nearly two million civilians were left without water in Aleppo after regime bombardment damaged a pumping station and rebels shut down another in retaliation. Ban warned the use of bunker buster bombs and other advanced munitions against civilians may amount to war crimes, after the army Thursday launched the offensive backed by Russian air raids that has cost around 100 lives. Top EU officials said that the attacks on civilians amount to a “breach of international humanitarian law,” and called for intensified peace efforts.