North Korean leader Kim Jong-il is reported to be making a trip to China, amid renewed speculation over who his successor will be. Yonhap news agency quoted a South Korean official saying there were signs that Kim Jong-il was using his special train to make the visit. The reports said he was accompanied by his son and possible heir Kim Jong-un. If confirmed, it would be Mr Kim's second trip to China this year, after a five-day visit in May. The reclusive leader rarely travels abroad. Beijing and Pyongyang generally only acknowledge such visits once they are over. Meanwhile, the former US President Jimmy Carter has spent night in Pyongyand on a mission to secure the release of an American man jailed there.