A Syrian Opposition senior commander said on Friday that Syrian regime forces would never be able to capture Aleppo’s opposition-held east.

Russian air strikes were proving of little help to regime ground forces in urban warfare, the deputy commander of the Fastaqim opposition group in Aleppo said. While air strikes have pounded much of the city, they have avoided frontlines where the sides are fighting in close proximity, apparently out of fear they could hit the wrong side, he said.

Opposition fighters were well prepared for a siege imposed this summer, and preparations for a counter attack were under way, Melhem Akidi told Reuters.

“Militarily there is no danger to the city of Aleppo,” he said, adding: “The more dangerous thing is the daily massacres by the regime that are targeting not just the people but the foundations of life in Aleppo.”

The assessments, on the eve of a meeting between U.S. and Russian foreign ministers in Switzerland to try to resume their failed efforts to find a diplomatic solution, point to a protracted battle for Aleppo.

Syria’s biggest city before the war has been divided into areas controlled by the regime and opposition forces for several years. The opposition-held east is the last major urban stronghold of the nationalist rebels fighting regime head Bashar al-Assad, and recapturing it would be a major strategic prize.

Pro-Assad forces, supported by Iranian-backed militias and Russian air power, announced a major offensive to capture the rebel-held part of the city on Sept. 22, unleashing firepower not previously seen in the 5-1/2-year long war.

The onslaught has killed several hundred people and flattened many buildings. Hospitals have also been hit, leading the United States and France to accuse Russia and the Syrian regime of war crimes. Moscow and Damascus say they are only targeting militants.