SEOUL (Reuters) - The United States sought Chinas help in persuading its long-time ally North Korea to abandon nuclear weapons, sending its envoy to Beijing on Wednesday as part of a campaign to press the North. The US envoy for North Korea policy, Stephen Bosworth, met South Korean officials in Seoul before heading to China. Washington hopes talks on dismantling North Koreas nuclear work can start soon, though a breakthrough may prove elusive. North Korea issued a statement demanding what it described as unconditional talks with the South and calling for an end to any actions that could cause one side to provoke the other on the divided peninsula. But it was uncertain the South would heed any such call less than two months after the North bombarded a South Korean island off disputed waters, killing four people. North Koreas reclusive and often unpredictable leaders have made repeated pledges in the past to regional powers on doing away with its nuclear program with little practical result.