World leaders: Nuclear terrorism a 'grave threat'

World leaders have called for closer co-operation to tackle the threat of nuclear terrorism at a summit on nuclear security in Seoul. South Korean President Lee Myung-bak said nuclear terrorism remained a "grave threat", while US President Barack Obama said action was key. Chinese President Hu Jintao urged the group to work together on the issue. The meeting has so far been dominated by North Korea's plan to launch a rocket next month. North Korea says the long-range rocket will carry a satellite. The US says any launch would violate UN resolutions and constitute a missile test. Iran's nuclear programme was also on the minds of the summit participants, with Mr Obama pledging to meet the leaders of Russia and China on the sidelines to work towards a resolution.