SEOUL (Reuters) - North Korean leader Kim Jong-il and his son and successor Jong-un visited the artillery base from where shells were fired at a South Korean island just hours before the attack, South Korean media reported on Thursday.

North Korea’s attack on Yeonpyeong Island that killed two South Korean marines and two civilians on Tuesday was probably ordered by Kim Jong-il himself, the Joongang Daily quoted a well-informed government source as saying.

Seoul government officials contacted by Reuters could not comment on the reports.

The United States says it believes North Korea’s actions were an isolated act tied to leadership changes in Pyongyang, and many experts say the North carried out the shelling to burnish the image of the inexperienced and little-known younger Kim.

The ailing leader is desperate to give a lift to his youngest son, named as heir apparent to the family dynasty in September, but who has little clear support in the military.

South Korean media reported the father and son had met General Kim Kyok-sik, the commander of the frontline fourth corps in charge of a Navy base in South Hwanghae province, just before the North shelled the island.

A member of the National Assembly’s Defense Committee said military intelligence obtained the information and was trying to figure out whether the visit was directly related to the attack, the Chosun Ilbo reported.

Just before the sinking of a South Korean warship in March, the South Korean military “had confidential information that Kim Jong-il met Kim Yong-chol, the director of the general reconnaissance bureau at the People’s Armed Forces, so now it’s focusing on the possibility of Kim Jong-il and his son approving the shelling of Yeonpyeong while meeting with Kim Kyok-sik,” he said.

JoongAng Daily quoted a source as saying that Kim visited the coastal artillery base in Gaemori from where the shells were fired with his son a day before the attack.

“This is circumstantial evidence that the attack was meticulously planned (by North Korea) beforehand,” said the source.

North Korea’s official Korean Central News Agency issued a report on Monday saying Kim Jong-il had made a trip to a fish farm in Yongyon, South Hwanghae province, and that he was accompanied by top military brass, including Jong-un.

There was no mention of any visit to military sites.

Yongyon is just a few kilometers from the North Korean coastal military base where the artillery was fired from, reports said.

North Korea has entered a potentially long and unpredictable period of leadership transition, with the elevation of Kim’s youngest son to the rank of general in a clear signal he is the chosen successor.

The media has begun celebrating Kim Jong-un as “the young general” -- even though his military experience appears to be zero.

Analysts have been warning since September that North Korea would likely carry out an act of brinkmanship to boost the younger Kim’s standing, to mirror the iron rule of his father.