ADEN - A suspected US drone attacked a convoy of Islamist militants in eastern Yemen overnight, killing three people, a local security official said on Thursday, as Washington intensifies its aerial campaign against fighters linked to al-Qaida.The official said the rocket hit the convoy in the Shibam area of the eastern Hadramout province and there was a series of explosions from a vehicle believed to be laden with explosives.Residents of the area told Reuters its three passengers were members of a militant cell. The accounts could not be independently verified.The United States has increasingly used drones against militants after they seized swathes of territory in the south of the country during a year of political upheaval that eventually toppled President Ali Abdullah Saleh.