BEIRUT (AP) — The Syrian army inched closer to seizing a central prison in the contested northern city of Aleppo Wednesday, with intense artillery shelling and military aircraft dropping dozens of crude bombs in the area and killing at least 50 rebel fighters, Syrian state media and opposition activists said.

The sprawling prison, along with its estimated 4,000 inmates, has been caught in the deadly stalemate of Syria’s civil war for months. Rebels have been besieging the facility for the past year, and have repeatedly barreled suicide car bombs into the front gates and clashed with guards and troops holed up inside in an effort to capture the prison.