Obama starts S Korea visit amid N Korea tensions

US President Barack Obama arrived in South Korea Sunday to hold talks with its leader and attend a 53-nation nuclear security summit, amid tensions with North Korea over its upcoming rocket launch. Obama, who landed at a US air base south of Seoul, was to meet President Lee Myung-Bak later Sunday for talks expected to be dominated by next month\'s planned launch, which has stirred international concern. Pyongyang says preparations are well advanced to put a peaceful satellite into orbit in mid-April. Washington and its allies say such an exercise would be a grave provocation and breach United Nations resolutions. The US says any launch would also breach a deal reached just weeks ago, under which the North accepted a partial nuclear freeze and a missile test moratorium in return for US food aid. Obama, who will attend a major summit in Seoul Monday and Tuesday on securing the world\'s nuclear stockpiles, was Sunday morning to visit the tense border between the two Koreas. The aim of the trip to the Demilitarised Zone is to express appreciation to the 28,500 US troops based in the South and stress US commitment to the South\'s security, White House officials have said