Four Palestinians killed and 16 others injured in a propane tank explosion occurred Monday morning in a residential building in the old city of Akka.The wounded Palestinians were transferred to hospitals in Nahariya and Haifa, as the condition of three of those injured in the blast were described as critical. Among the injured are three children and a firefighter hurt during the rescue efforts.The Israeli police initiated an investigation into the incident, and the police suspect the fire was set intentionally, in an attempt to harm cellar telephone equipment being housed within the building's top floor.