Commemorations are being held in South Korea to mark the 60th anniversary of the outbreak of the Korean War. North Korean tanks and troops swept south on 25 June 1950, starting a three-year conflict that claimed an estimated four million lives. The US led the United Nations in support of the South while China and Russia backed the North. The war ended with a ceasefire rather than a peace treaty, leading to almost constant political tension ever since. North Korea still disputes the widely held view that it attacked first.