BAMAKO - Mali's interim president, Dioncounda Traore, reappointed his prime minister on Sunday, calling upon him to name a new government of national unity within 72 hours to form a united front against Islamists in the north.Once considered a democratic success story in a long troubled region, the West African nation has been split in two since a March 22 coup paved the way for a military advance by northern separatists and al Qaeda-linked Islamists.Traore and Prime Minister Cheick Modibo Diarra, a former NASA astrophysicist and political novice, were named as part of a deal that saw a military junta return leadership of the country to a civilian caretaker government.