South Korea's defense minister resigned Thursday, two days after an artillery attack by North Korea killed four people on small island near their disputed frontier.

The move came as President Lee Myung-bak vowed to send more troops to the island and as residents tried to salvage belongings from its blackened wreckage. Pyongyang warned of additional attacks if provoked.

Yim Tae-hee, presidential chief of staff, said Lee accepted the resignation of Defense Minister Kim Tae-young and said a new chief was to be announced Friday. The outgoing minister will keep his job until his replacement is announced, he said.

In May, the outgoing minister offered to resign following the deadly sinking of a South Korean warship blamed on North Korea. Yim said the president delayed accepting Kim's resignation offer until Thursday. He said Lee decided to accept the resignation because of recent military incidents and to improve the military's atmosphere.

The North's bombardment of the tiny South Korean island of Yeonpyeong on Tuesday was the first such attack on a civilian area, raising fears of an escalation leading to a new war on the Korean peninsula. Seoul and Washington ratcheted up pressure on China to rein in its ally North Korea, and China urged both sides to show restraint.

The South Korean president also replaced his aide in charge of defense affairs, Yim said.

The defense minister's resignation came after fierce criticism of the government's response to the North Korean shelling. Yonhap news agency reported that lawmakers in the ruling and opposition parties demanded his dismissal as well as those of military leaders and some presidential aides.

Reporters allowed for the first time onto Yeonpyeong Island saw streets strewn with charred debris and wrinkled metal. Blackened drink bottles lay besides remains 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 had fled, but restaurant owner Lee In-ku, 46, joined a handful of villagers collecting belongings from houses that were not fully destroyed.

"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."

The president said during an emergency meeting of top officials in Seoul that the country "should not let our guard down," presidential spokesman Hong Sang-pyo said. "I think a similar North Korean provocation could come at any time," he quoted Lee as saying.

Hong said that South Korea will increase ground troops on Yeonpyeong and four other islands in western waters in response to this week's attack, reversing a 2006 decision calling for an eventual decrease. He declined to discuss specifics for the increase, but said troops there currently amount to about 4,000.

South Korean troops had returned fire and scrambled fighter jets in response to Tuesday's attack.

In addition to the two marines and two civilians killed in the exchange, at least 18 people _ most of them troops _ were wounded on Yeonpyeong, which is 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.