YEONPYEONG ISLAND, South Korea — A defiant flash of North Korean artillery within sight of the island that it attacked this week sent a warning signal to Seoul and Washington: The North is not backing down.

The apparent military drill Friday came as the top U.S. commander in South Korea toured Yeonpyeong island to survey the wreckage from the rain of artillery three days earlier. As a U.S. nuclear-powered aircraft carrier headed toward the Yellow Sea for exercises next week with South Korea, the North warned that the joint maneuvers will push the Korean peninsula to the "brink of war."

South Korea’s government, meanwhile, struggled to recoup from the surprise attacks that killed four people, including two civilians, and forced its beleaguered defense minister to resign Thursday. President Lee Myung-bak on Friday named a former chairman of the Joint Chiefs of Staff to the post.

Tensions have soared between the Koreas since the North’s strike Tuesday destroyed large parts of Yeonpyeong in a major escalation of their sporadic skirmishes along the disputed sea border.

The attack — eight months after a torpedo sank a South Korean warship, killing 46 sailors — has laid bare Seoul’s weaknesses in defense 60 years after the Korean War. Lee has ordered reinforcements for the 4,000 troops on Yeonpyeong and four other Yellow Sea islands, as well as top-level weaponry and upgraded rules of engagement.

The heightened animosity between the Koreas comes as the North undergoes a delicate transition of power from leader Kim Jong Il to his young, inexperienced son Kim Jong Un, who is in his late 20s and is expected to eventually succeed his ailing father.

Washington and Seoul have pressed China to use its influence on Pyongyang to ease tensions amid worries of all-out war. A dispatch Friday from Chinese state media saying Beijing’s foreign minister had met the North Korean ambassador appeared to be an effort to trumpet China’s role as a responsible actor and placate the U.S. and the South.

The North sees the U.S.-South Korean drills scheduled to start Sunday as a major military provocation. Pyongyang unleashed its anger over the planned exercises in a dispatch earlier Friday.

"The situation on the Korean peninsula is inching closer to the brink of war," the report in the North’s official Korean Central News Agency said.

A North Korean official boasted that Pyongyang’s military "precisely aimed and hit the enemy artillery base" as punishment for South Korean military drills — a reference to Tuesday’s attack — and warned of another "shower of dreadful fire," KCNA reported.

China expressed worry over any war games in waters within its exclusive economic zone, though the statement on the Foreign Ministry website didn’t mention the drills starting Sunday. That zone extends 230 miles (370 kilometers) from China’s coast and includes areas south of Yeonpyeong cited for possible maneuvers, although the exact location of the drills is not known.

North Korea does not recognize the maritime border drawn by the U.N. in 1953, and considers the waters around Yeonpyeong Island its territory.

Yeonpyeong Island, home to South Korean military bases as well as a civilian population of about 1,300 people, lies only seven miles (11 kilometers) from North Korean shores.

The U.S. commander in South Korea, Gen. Walter Sharp, said during a visit to the island that Tuesday’s attack was a clear violation of the armistice signed at the end of the three-year Korean War.

"We at United Nations Command will investigate this completely and call on North Korea to stop any future attacks," he said.

Washington keeps more than 28,000 troops in South Korea to protect its ally — a sore point for North Korea, which cites the U.S. presence as the main reason behind its drive to build nuclear weapons.

Dressed in a heavy camouflage jacket, army fatigues and a black beret, Sharp carefully stepped down a devastated street strewn with debris and broken glass. Around him were charred bicycles and shattered bottles of soju, Korean rice liquor.

On Friday, Associated Press photographers at an observation point on the northwest side of Yeonpyeong heard explosions and saw at least one flash of light on the North Korean mainland.

There were no immediate reports of damage. Only a few dozen residents remain on Yeonpyeong, with most of its population fleeing in the hours and days after the attack as authorities urged them to evacuate.

Many houses were burned out, half-collapsed or flattened, and the streets were littered with shattered windows, bent metal and other charred wreckage. Several stray dogs barked as they sat near destroyed houses. South Korean marines carrying M-16 rifles patrolled along a seawall at dawn.

About 200 South Koreans held a rally Friday in Seoul to denounce the government’s response to the attack as too weak. Similar recriminations have come from opposition lawmakers and even members of Lee’s own party, leading to the resignation of Defense Minister Kim Tae-young on Thursday.

There also has been intense criticism that Yeonpyeong was unprepared for the attack and that the return fire came too slowly. Lee named former Joint Chiefs of Staff chairman Kim Kwan-jin to the post, the president’s office said Friday.

While there is some shock at the extent of the damage the North Koreans were able to inflict, most South Koreans want the threat to be contained, not aggravated, and the government response has been muted and cautious, following an initial angry threat from Lee.

The president, dressed in a black suit, visited a military hospital in Seongnam near Seoul on Friday to pay his respects to the two marines killed in the North Korean attack.

Lee laid a white chrysanthemum, a traditional symbol of grief, on an altar, burned incense and bowed before framed photos of the two young men. Consoling sobbing family members, he vowed to build a stronger defense.

"I will make sure that this precious sacrifice will lay the foundation for the strong security of the Republic of Korea," he wrote in a condolence book, according to his office.

South Korea assured a meeting of the European Olympic Committees on Friday that it would be able to ensure security at the 2018 Winter Games if it’s picked. The Pyeongchang 2018 bid committee presented its case Friday in Belgrade.

Foster Klug reported from Seoul. AP writers Christopher Bodeen in Beijing and Kwang-tae Kim, Kelly Olsen and Jean H. Lee in Seoul also contributed to this report.