KABUL — A car bomber struck a coalition convoy outside a base in southern Afghanistan Thursday, hours after a visit by Defense Secretary Leon E. Panetta.

There were no indications the suicide bombing near Kandahar Air Field was connected to the visit by Panetta, who arrived in Kabul on Wednesday. His day trip to Kandahar on Thursday was not publicized in advance and garnered little media attention as it was taking place. Panetta never left the base.