South Korea's defence minister has resigned amid criticism of his handling of North Korea's shelling of an island near their disputed maritime border.
President Lee Myung-bak will name Kim Tae-young's successor on Friday.
Tuesday's barrage left two South Korean civilians and two marines dead, and sent regional tensions soaring.
South Korea has increased troop numbers on Yeonpyeong and other nearby islands, and announced more rigorous rules of engagement for future incidents.
Mr Kim had been urged to step down by legislators from both governing and opposition parties over his handling of the shelling.
In his resignation statement, the minister said he took full responsibility.
More powerful response
The government also said it was changing its rules of engagement to allow it to respond more forcefully to similar incidents. The old rules have been criticised as too passive.
The BBC's Chris Hogg in Seoul says the cabinet had decided that under the old rules of engagement there was too much emphasis on preventing a military incident escalating into something worse.
In future, the South would implement different levels of response, depending on whether the North attacked military or civilian targets, a presidential spokesman said.
A senior government official told the BBC that Seoul wanted to be more flexible in order to keep the North Koreans guessing as to their response.
The South Korean broadcaster, KBS, said the new rules called for the South to fire back "with shots two to three times more powerful than the enemy artillery".
North Korea meanwhile threatened further military action if the South continued on its "path of military provocation", the official KCNA news agency reported.
Pyongyang has blamed Seoul for this week's incident on Yeonpyeong, insisting it did not fire first. The South was holding military exercises in the area at the time, and returned fire when the North's shells began to land.
The North also accused the United States of stoking tensions - saying it helped draw up the "illegal" western maritime border between the two Koreas.
About 28,000 US troops are stationed in South Korea.
Naval exercisesThe clash was one of the worst incidents between the two Koreas, who remain technically at war because the 1950-53 Korean War ended without a peace treaty.
The US and South Korean militaries are to hold joint naval exercises, which will include US aircraft carrier USS George Washington, south of Yeonpyeong in the coming days.
The Chinese foreign ministry has expressed "concern" over the exercises.
"We oppose any act that undermines peace and stability on the peninsula," it said.
Beijing, Pyongyang's main ally, has been under pressure to use its influence to ease tensions.
Chinese Premier Wen Jiabao, who is in Moscow, earlier described the situation on the peninsula as "grim and complicated".
Mr Wen repeated his view that the six-party talks on the North's nuclear programme should be resumed as soon as possible, a position shared by Pyongyang.
South Korea, the US and Japan have said the negotiations should not restart until the North stops uranium enrichment work and apologises for its alleged torpedoing of a South Korean warship in March, which killed 46 sailors.
A visit by Chinese Foreign Minister Yang Jiechi to South Korea, which had been due on Friday, has also been postponed. The delay was put down to "scheduling" issues.
source : bbc.co.uk
