DAMASCUS - A car bomb killed 13 people in central Damascus on Sunday as President Bashar Assad told an international mediator seeking a truce in Syria's civil war that the key to any political solution was to stop arming rebels.The bomb exploded outside a police station in the mainly Christian central Bab Touma district of the capital while Assad held talks with United Nations-Arab League envoy Lakhdar Brahimi, who is pushing for a temporary ceasefire to mark the Islamic festival of Id al-Adha.State news agency SANA said the president said Syria supported "any sincere effort to find a political solution to the crisis, based on respect for Syrian sovereignty and rejecting foreign intervention."