A mine exploded under a U.S. Humvee in a Taliban stronghold of southeastern Afghanistan, wounding two American soldiers, officials said Tuesday. The incident came within hours of the death of two U.S. soldiers in a fire-fight, adding to security concerns less than three weeks before landmark national elections. The mine explosion hit one of a group of American Humvees on patrol in Shinkay district of Zabul province on Monday, Gov. Khial Mohammed said.