North Korea demanded Friday that Seoul apologize for what it claimed were slanderous remarks about its leader Kim Jong-un by a South Korean official, calling it an unpardonable provocation. The official, who heads a think tank affiliated with Seoul's spy agency, told a group of ruling party lawmakers Tuesday that Kim is instituting a reign of terror in reference to the execution of his once-powerful uncle Jang Song-thaek in December on charges of treason. "South Korea should apologize for grave provocations and take responsible steps to ensure similar accidents do not recur, if it has the intention to build trust and improve North-South relations," said the Committee for the Peaceful Reunification of Korea that handles inter-Korean affairs.