U.N. Secretary-General Ban Ki-moon condemned the callous terrorist attack against civilians in northeast Beirut on Tuesday, as Lebanon prepared to commemorate the assassination of former Prime Minister Rafiq Hariri, U.N. spokeswoman Michele Montas said. The United Nations strongly rejects attempts to secure political objectives through violence and the killing of innocent civilians, Montas told reporters. Two bombs hit two buses in the Christian part of the capital, killing three people and wounding at least 18. The secretary-general stresses that there must be an end to impunity and appeals to all Lebanese to maintain unity in the face of such attempts to undermine the country s stability, said Montas. A U.N.-sponsored probe into the murder of Hariri and 21 others is scheduled to end by June unless top prosecutor Serge Brammertz asks for an extension. Brammertz is scheduled to brief the U.N. Security Council next month on his findings, with a comprehensive report by summer.