North Korean leader Kim Jong Il and his son and successor Jong Un reportedly 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, according to a Reuters report.
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, according to Reuters.
Meanwhile, North Korea warned of more attacks if South Korea takes any military actions following the North’s deadly artillery attack.
South Korean President Lee Myung-bak vowed to send more troops to the front-line South Korean island as his defense minister resigned amid intense criticism following the deadly assault by Pyongyang. The announcement came as residents tried to salvage belongings from the blackened wreckage of their homes.
Hours before Defense Minister Kim Tae-young's resignation, lawmakers had lashed out at the government, claiming officials were unprepared for Tuesday's attack and that the military response to the North's barrage was too slow. Even those in Lee's ruling party demanded Kim's dismissal as well as those of military leaders and some presidential aides.
Lee accepted Kim's resignation and a new defense chief will be announced Friday, presidential chief of staff Yim Tae-hee said.
Skirmishes between the Korean militaries are not uncommon, but North Korea's heavy bombardment of Yeonpyeong Island was the first on a civilian area, raising fears of an escalation that could lead to a new war on the Korean peninsula. South Korean troops had returned fire and scrambled fighter jets in response.
Seoul and Washington ratcheted up pressure on China to rein in its ally North Korea, and China on Thursday urged both sides to show restraint.
Reporters allowed for the first time onto the island found streets strewn with broken glass and charred debris. Blackened beer bottles lay beside what was left of a supermarket as coast guard officers patrolled in pairs past deserted offices and schools used by relief workers for meetings and meals.
Many residents fled as quickly as they could, but restaurant owner Lee In-ku, 46, joined a handful of villagers trying to salvage belongings from half-destroyed homes.
"It was a sea of fire," Lee said of Tuesday's attack. "Many houses were burning and many people were just running around in confusion. It was real chaos."
At an emergency meeting in Seoul on Thursday, President Lee ordered top-level weapons for troops manning the tense Yellow Sea, a presidential aide said.
"We should not ease our sense of crisis in preparation for the possibility of another provocation by North Korea," presidential spokesman Hong Sang-pyo quoted Lee as saying. "A provocation like this can recur any time."
Hong said South Korea will sharply raise the number of ground troops on Yeonpyeong and four other islands, reversing a 2006 decision to draw down forces. He declined to discuss specifics but said troops there currently are about 4,000.
He also said the military would change its rules of engagement to better counter North Korean provocations.
The defense minister's resignation came hours after he visited Yeonpyeong, home to military bases as well as a fishing community of 1,300 residents. It lies about 50 miles (80 kilometers) from South Korea's western port of Incheon, and just 7 miles (11 kilometers) from North Korean shores
Two marines and two civilians were killed in Tuesday's exchange, and at least 18 people — most of them troops — were wounded.
Marine Lt. Col. Joo Jong-wha acknowledged that the island is acutely short of artillery, saying it has only six pieces, the howitzers used in Tuesday's skirmish.
"In artillery, you're supposed to move on after firing to mask your location so that they don't strike right back at you. But we have too few artillery," he said on Yeonpyeong.
Military officials analyzing debris have not ruled out North Korea's use of thermobaric bombs, which burn more violently and increase casualties and property destruction, a Joint Chiefs of Staff official said. He asked not to be identified, saying he was not authorized to speak to reporters.
The two Koreas are required to abide by an armistice signed at the close of their three-year war, but the North does not recognize the maritime line drawn by U.N. forces in 1953 and considers South Korean maneuvers near Yeonpyeong island a violation of its territory. South Korea was conducting firing drills, though not in North Korea's direction, when the North Korean artillery barrage came Tuesday.
The attack added to animosity from the March sinking of a South Korean warship in nearby waters that killed 46 sailors in the worst military attack on the nation since the Korean War.
The defense minister also offered to resign following that incident, but the president refused.
The shelling occurred as North Korea is undergoing a delicate transition of power from leader Kim Jong Il to his young son Kim Jong Un. The son, who is in late 20s, was made a four-star general and nominated to high-ranking Workers' Party posts in the first steps toward eventually succeeding his father.
North Korea's state news agency reported Monday, a day before the attack, that the elder Kim and the son and other key political and military figures visited duck and fish farms in an area about 60 miles (100 kilometers) from the base where the artillery barrage was launched.
The attack alarmed world leaders, including President Barack Obama, who reaffirmed plans for joint maneuvers with Seoul involving a nuclear-powered aircraft carrier in the Yellow Sea starting Sunday.
North Korea made no specific mention of those exercises but warned Thursday of "strong physical retaliations without hesitation if South Korean warmongers carry out reckless military provocations."
Pyongyang also said Washington was partly to blame for letting South Korea hold artillery drills that it said prompted the artillery barrage.
Washington "should thoroughly control South Korea," it said. The warning was issued by North Korea's military mission at the truce village of Panmunjom and carried by the official Korean Central News Agency.
Meanwhile, the Obama administration urged China to rein in ally North Korea.
"We really think it's important for the international community to lead, but in particular China," said Adm. Mike Mullen, chairman of the Joint Chiefs of Staff in Washington.
South Korea said it will increase diplomatic efforts to get China, which supplied North Korea with troops during the Korean War and remains its main ally and biggest benefactor, to put pressure on Pyongyang.
Chinese Premier Wen Jiabao called on all sides to show "maximum restraint" and called again for renewed six-nation talks aimed at persuading North Korea to dismantle its nuclear programs. Wen said those talks, involving the two Koreas, China, Russia, Japan and the United States, are the best way to ensure stability on the peninsula and its denuclearization.
In Seongnam just outside Seoul, military officers, family members and dignitaries mourned the two marines killed in the attack, laying flowers and burning incense at an altar. Funerals are to take place Saturday.
Former President Kim Young-sam used the occasion to criticize North Korean leader Kim Jong Il, saying he is "not a human," and said that a China that defends North Korea "can never be trusted," Yonhap said.
The Associated Press contributed to this report.