U.S. Defense Secretary Leon Panetta flew into Afghanistan on Wednesday, making him the first high-ranking American official to visit the country since a U.S. soldier was detained on suspicion of killing 16 Afghan men, women and children in their homes Sunday.

Also Wednesday, a huge explosion killed eight people in Helmand province, which Panetta was visiting, but he was not affected.

The massive roadside blast ripped through a minivan, leaving its victims unrecognizable, the Helmand government said. The government blamed "terrorists" for the bombing.