"How many more people will be killed if the current situation continues," Mr Ban asked at a donors' conference in Kuwait, aimed at raising money for UN humanitarian work.
"I appeal to all sides and particularly the Syrian government to stop the killing. In the name of humanity, stop the violence," the UN leader said.
Syrian opposition activists said at least 65 people were found shot dead with their hands bound in Aleppo, the latest reported massacre over the course of 22 months of conflict.
They blamed militiamen loyal to President Bashar al Assad, while the government blamed the Islamist rebel Nusra Front. The UN say more than 60,000 people have been killed since the conflict began as a peaceful movement for democratic reform.
Four million Syrians inside the country need food, shelter and other aid, and more than 700,000 more are estimated to have fled to countries nearby.
UN humanitarian chief Valerie Amos said: "We are watching a human tragedy unfold before our eyes."