South Korea's president urged North Korea Sunday to end its military provocations but Pyongyang threatened the "severest punishment" over Seoul's massive joint war games with the United States. The rivals exchanged tit-for-tat warnings as the South unveiled a roadmap for the reunification of the Korean peninsula on the eve of a 10-day exercise involving some 56,000 South Korean and 30,000 American soldiers. "It is about time Pyongyang looked straight at reality, made a courageous change and came up with a drastic decision," South Korean President Lee Myung-Bak said. The Koreas "need to overcome the current state of division and proceed with the goal of peaceful reunification," he said in a speech to celebrate Korea's liberation from Japanese colonial rule in 1945.