Two men were killed when a bomb they were planting exploded outside a regional electoral campaign office of Afghanistan's US-backed President Hamid Karzai, an official said on Saturday. The bombers had targeted Mr Karzai's office in Pul-e-Alam, some 60 kilometres southeast of the capital Kabul, on Thursday night, he said. "One of the bombers was beheaded and the other one died from injuries after the bomb exploded," said provincial governor Mohammed Aman Hamimi.