IMPHAL: A powerful bomb exploded and another was detected at two places on the road leading to Imphal airport minutes before Prime Minister Atal Behari Vajpayee landed here on Friday to commence his two-day visit to Manipur. The sources said no damage was caused in the bomb explosion triggered by underground militants in the Kwakeithel Heinoukhongnembi area around 10.30 am. Earlier, another powerful bomb was detected on the road in Khwakeithel-Tiddim ground area, they said.