Pyongyang opposes war, but if Seoul chooses military confrontation or makes a preemptive strike, then Pyongyang's nuclear forces will have to attack, the sister of leader Kim Jong Un said on Tuesday.

Kim Yo Jong, a senior official in the government and ruling party, said it was a "very big mistake" for the Republic of Korea (ROK)'s minister of defense to make recent remarks discussing attacks on the Democratic People's Republic of Korea (DPRK), state news agency KCNA reported.

ROK Defense Minister Suh Wook said on Friday that his country's military has a variety of missiles with significantly improved firing range, accuracy and power, with "the ability to accurately and quickly hit any target in (the) DPRK."

Pyongyang has test-fired a range of increasingly powerful missiles this year, and officials in Seoul and Washington fear it may be preparing to resume testing nuclear weapons for the first time since 2017 amid stalled negotiations.

Kim and another DPRK official issued earlier statements on Sunday condemning those remarks, and warned that Pyongyang would destroy major targets in Seoul if it takes any "dangerous military action" such as a preemptive strike.

In her second statement, on Tuesday, Kim said Pyongyang opposes war, which would leave the peninsula in ruins, and does not view ROK as its principal enemy.

"In other words, it means that unless the ROK army takes any military action against our state, it will not be regarded as a target of our attack," she said.

"But if the ROK, for any reason – whether or not it is blinded by misjudgment – opts for such military action as 'preemptive strike' touted by (Suh Wook), the situation will change," Kim added. "In that case, the ROK itself will become a target."

If the ROK military violates even an inch (2.5 cm) of DPRK territory, it will face an "unimaginably terrible disaster" and the DPRK's nuclear combat force will have to inevitably carry out its duty, she said.

"This is not just a threat. This is a detailed explanation of our reaction to possible reckless military action by ROK," Kim said, noting that Seoul can avoid this fate by dropping any "fantastic daydream" of launching a preemptive attack on a nuclear-armed state.