BEIRUT – The Syrian regime pounded Aleppo with warplanes and artillery shelling Saturday as ground forces seeking to regain momentum in the country’s largest city advanced on three neighborhoods, activists said.

The new fighting came as Russia soundly rejected U.S. calls for increased pressure on Syrian President Bashar Assad to relinquish power, citing its commercial interests.

Shelling and air raids against the eastern Helwaniyeh neighborhood caused a large number of casualties, according to the Britain-based Syrian Observatory for Human Rights and another activist group called the Local Coordination Committees. Amateur videos showed wounded people bleeding on the floor of a crowded makeshift hospital as they received treatment.