South Korea said yesterday it would send more troops and guns to frontline islands, as North Korea warned it could follow up this week's deadly shelling with more attacks.
Pyongyang's fresh warning came as a US aircraft carrier headed for the tense peninsula to join war games to be staged as a show of force to the nuclear-armed communist state.
The North's unprecedented artillery bombardment of Yeonpyeong island on Tuesday killed two marines and two civilians, injured 18 more people and turned homes into charred ruins.
It claimed its first political victim when the South's Defence Minister Kim Tae-Young resigned, following growing criticism that Seoul's military and government reacted too softly to the assault.
The government said yesterday it would revise its rules of engagement, allowing troops to hit back harder if necessary.
Tuesday's attack was the first time the North had shelled a civilian area since the 1950-53 war.
It provoked the worst crisis on the peninsula in years, with the international community agonising over how to respond. South Korea and the United States, among others, pressed China to rein in its neighbour.
The North accused the United States and its "warmongering South Korean puppets" of provoking the attack. It said South Korea's military in an exercise fired shells within what the North claims as its own waters.
The regime said that if the South commits "another reckless military provocation, our army will carry out second and third rounds of powerful physical retaliatory strikes without hesitation".
On the island hit by the North's fiery hail of rockets and missiles, grim-faced soldiers trudged through broken glass, debris and the blackened wreckage of homes.