South Korea has measures in place to reduce Pyongyang, the North Korean capital, "to ashes" if Kim Jong Un's regime shows any signs that it is planning to carry out a nuclear attack.
"Every Pyongyang district, particularly where the North Korean leadership is possibly hidden, will be completely destroyed by ballistic missiles and high-explosive shells as soon as the North shows any signs of using a nuclear weapon", a source in the South Korean military told the Yonhap news agency.
"In other words, the North's capital city will be reduced to ashes and removed from the map", the source said.
Tensions are once again high on the Korean Peninsula, two days after North Korea carried out its fifth underground nuclear test.
The blast, at the North's Punggye-ri nuclear proving grounds, was initially detected as a magnitude-5 earthquake but subsequently confirmed as Pyongyang's largest-ever nuclear detonation.
Within hours, North Korean state media announced that the test had been a success and demonstrated the regime's ability to mount nuclear warheads on strategic ballistic missiles.
The international community is considering its response to the latest provocation by the North, with the United States, South Korea and Japan leading the calls for even more sanctions to be imposed.
South Korea has chosen to make it clear to its northern neighbour, however, that it is ready and able to act should it conclude that a nuclear attack is imminent. The Defence Ministry put forward a plan, titled Korea Massive Punishment and Retaliation, to the South Korean Parliament last week, with part of the plan calling for "wiping a certain section of Pyongyang completely off the map".
The operation calls for pre-emptive bombing attacks against locations that Kim is known to frequent. The strike would also target his top military commanders.
South Korea intends to use domestically produced surface-to-surface ballistic missiles, the most advanced of which - the Hyunmoo 3 - has a range of more than 965km.
The South Korean military is developing another version of the missile, with greater range and payload.
There are also growing calls in the South for Seoul to ask the US to once again deploy nuclear weapons on its territory.
Ultimately, analysts at the Sejong Institute, called for South Korea to develop and deploy an independent nuclear strike capability.
A defiant North Korea has restated its demand for recognition as a "legitimate" nuclear-armed state.
Every Pyongyang district, particularly where the North Korean leadership is possibly hidden, will be completely destroyed by ballistic missiles and high-explosive shells as soon as the North shows any signs of using a nuclear weapon
The North also vowed to increase its nuclear strike force "in quality and in quantity".
In Japan, a visiting senior US envoy said Washington and Tokyo were seeking "the strongest possible" measures in response.
North Korea insists that its missile and nuclear tests are necessary to counter what it says is a US nuclear threat to its independence.
A statement from a foreign ministry spokesman in Pyongyang mocked US President Barack Obama's "totally bankrupt" policy on the country.
"Obama is trying hard to deny the DPRK's (North Korea's) strategic position as a legitimate nuclear weapons state but it is as foolish an act as trying to eclipse the sun with a palm," said the statement quoted by the official KCNA news agency.
Sung Kim, the US State Department's special representative for North Korea policy, said Washington and Tokyo would work closely in the Security Council and beyond "to come up with the strongest possible measure against North Korea's latest action".
He also suggested the US may launch its own unilateral sanctions in response to "the provocative and unacceptable behaviour by the North Koreans".
- additional reporting AFP