(Reuters) – At least 65 people were found shot dead with their hands bound in the northern Syrian city of Aleppo on Tuesday in a “new massacre” in the near two-year revolt against President Bashar al-Assad, activists said.

Opposition campaigners blamed the government but it was impossible to confirm who was responsible. Assad’s forces and rebels have been battling in Syria’s commercial hub since July and both have been accused of carrying out summary executions.

U.N.-Arab League mediator Lakhdar Brahimi told the U.N. Security Council “unprecedented levels of horror” had been reached in Syria, and that both the government and rebels had committed atrocious crimes, diplomats said.

He appealed to the 15-nation council to overcome its deadlock and take action to help end the civil war in which Syria is “breaking up before everyone’s eyes”.

More than 60,000 people are estimated to have been killed in the war, the longest and deadliest of the revolts that began throughout the Arab world two years ago.

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