UPDATE 1730 GMT: The spin out of Seoul is that the President's inner circle of ministers, in their emergency meeting,decided that old rules of engagement put too much emphasis on prevention of escalation. In future, South Korea will implement different levels of response, depending on whether the North attacked military or civilian targets, but the new rules call for retaliation "with shots two to three times more powerful than the enemy artillery".
UPDATE 1420 GMT: China's Foreign Minister Yang Jiechi has cancelled a visit to Seoul on Friday. Chinese officials claimed a scheduling conflict, but South Korean Foreign Ministry spokesman Kim Young-sun indicated Seoul has concerns.
UPDATE 1115 GMT: President Lee Myung-Bak has accepted the resignation of South Korea's Minister of Defense,Kim Tae-Young.
UPDATE 0945 GMT: South Korea has extended the ban on visits to North Korea.
Eight South Koreans will be allowed to cross the border on Friday to deliver basic supplies to South Koreans staying at a joint industrial park in the North Korean border town of Kaesong. About 680 South Koreans are at the park, which employs 44,000 North Korean workers.
UPDATE 0715 GMT: Almost all of the remaining 1700 residents of Yeonpyeong Island will evacuate ahead of Sunday's US-South Korea military exercise.
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Both North Korea and South Korea have struck further postures after Tuesday's artillery barrage by the North upon Yeonpyeong Island, which killed four people.
Pyongyang has threatened new attacks, blaming the US as well as South Korea for the Tuesday clash, and rejected any talks. The South Korean President's office, after a meeting with ministers dealing with security and the economy, said Seoul would "sharply bolster its military arsenal" in the Yellow Sea and revise its rules of engagement in light of the North Korean assault.
Hwang Jong-Bum, writing for The Hankyoreh, assesses that President Lee Myung-bak is striking a tougher pose, moving from emphasis on "ensuring there is no escalation" to "being resolute" because of domestic anger over his initial response.
Meanwhile, the Obama Administration talked down the clash and asked China to intervene with a strong statement against Pyongyang's attack.
State Department spokesman P.J. Crowley said North Korea's action was premeditated and violated the 1953 armistice, but he added that US officials do not believe Pyongyang is preparing for a war: "This was in our view a one-off, premeditated act....Without getting into intelligence matters, we don't see that North Korea is preparing for an extended military confrontation."
Crowley added that Washington is engaged in wide-ranging diplomacy with Beijing and others and hopes to speak directly to North Korea within the framework of post-armistice contacts. He specifically said, as China has influence with North Korea, the US expects Beijinig to be clear on where the blame rests in this incident.