South Korean President Lee Myung-bak has named a former chairman of the Joint Chiefs of Staff as his new defense minister.
Officials say retired general Kim Kwan-jin replaces Kim Tae-young, who resigned Thursday, following criticism of a slow response to Tuesday's deadly North Korean artillery attack.
Also on Friday, the American commander of United Nations Command, General Walter L. Sharp, visited the island of Yeonpyeong to speak with military commanders and observe the damage caused by the North's attack.
He called for the North to refrain from more attacks and meet with the U.N. Command immediately to discuss the incident.
The North's state Korean Central News Agency turned up the rhetoric Friday, saying joint South Korea - U.S. drills are a reckless plan by "trigger-happy elements" aimed at North Korea. Pyongyang has used such language frequently in the past to condemn military exercises in South Korea.
Fresh artillery fire was heard in the North Friday, but a spokesman for the South's Joint Chiefs of Staff said no projectiles landed on South Korean territory.
Two South Korean marines and two civilians were killed and at least 18 people were wounded in the attack on Yeonpyeong near the disputed border in the Yellow Sea.
South Korea said Thursday it is beefing up military forces on the islands near the Yellow Sea border with North Korea. Officials also say they will revise rules of military engagement to permit a more aggressive reply to future attacks.
Pyongyang has threatened additional attacks if, as it said, there are further provocations.
North Korea's closest ally, China, Thursday repeated its call for both sides to exercise restraint.
Beijing has been under international pressure to use its influence to rein in its neighbor. A spokesman for China's foreign ministry, Hong Lei, told reporters Thursday that China wants parties to work towards creating conditions for resuming six-nation talks on North Korea's disarmament. Pyongyang abandoned those talks last year after the United Nations imposed tough new sanctions on the regime.
North Korea fired about 100 shells at Yeonpyeong Tuesday. Pyongyang said the attack was a response to what it called a provocative South Korean military drill in which shells were fired from the island. North Korea claims sovereignty over the island and surrounding waters.
South Korea retaliated about 10 minutes later by firing 80 shells from K-9 howitzers at the North Korean coastal artillery that launched the attack.
U.S. Secretary of State Hillary Clinton reiterated Washington's commitment to its alliance with South Korea in a phone call Thursday to her South Korean counterpart, Kim Sung-hwan.
Reporters who visited Yeonpyeong Thursday saw damaged homes and streets strewn with broken glass and debris. Most of the island's 1,600 residents fled to the South Korean mainland after the attack.
Some information for this report was provided by AP, AFP and Reuters.