The leader of North Korea's military government appeared to be travelling to China Thursday, a South Korean news report said.
Kim Jong Il was reportedly on his way to Beijing by train, in what would be his second visit this year, the Yonhap News agency said, citing a senior South Korean government official who requested anonymity, dpa reports.
"Signs have been detected that Chairman Kim visited China early Thursday morning," the official was quoted as saying, referring to Kim's official position as Chairman of the National Defense Commission.
"We are still trying to grasp his exact destination and the purpose of the visit," the official added.
The trip came among speculation that 68-year-old Kim, who is said to have suffered a stroke in 2008, was preparing to hand power to his third son Kim Jong Un.
Pyongyang's nuclear disarmament was also thought to be on the agenda.
A Chinese envoy visited Pyongyang last week to discuss the possible resumption of the six-party talks on North Korea's nuclear programme, which include the US, Japan, Russia and South Korea.
The meetings "reached a full consensus of views," the North's state-run media said.
North Korea, which walked away from the talks in April 2009 over renewed sanctions, has repeatedly said it is willing to return to the table, but has not proposed a concrete date or venue.
The visit by Kim would be the first time he has travelled to China twice in one year, after he met Chinese President Hu Jintao in May. His trips to China are only officially confirmed once they are over, reportedly out of security concerns.