Kim Yo Jong's warning, carried in state media, was her second angry retort in three days to comments made by South Korea's defence chief Suh Wook last week.

They come as North Korea has resumed its sanctions-breaking weapons tests with an unprecedented blitz this year, last month firing its first intercontinental ballistic missile at full range since 2017.

Suh had said Friday that South Korea's military had missiles with "the ability to accurately and quickly hit any target in North Korea when there are clear signs of North's missile launch".

In response, Kim Yo Jong said it was a "very big mistake" for "lunatic" Suh to have discussed a pre-emptive strike against a nuclear power, according to the report in KCNA.

"In case South Korea opts for military confrontation with us, our nuclear combat force will have to inevitably carry out its duty," said Kim Yo Jong, who is a key policy advisor in Pyongyang.

She said the "primary mission" for her country's nuclear forces was to act as a deterrent, but if an armed conflict were to break out, such weapons will be used for "eliminating the enemy's armed forces at a strike".

As a result of this "dreadful attack", South Korean forces will face a "miserable fate little short of total destruction and ruin", she said.

"We do not regard (them) as (a) match for our armed forces," she said, referring to South Korea's military.

Her latest comments follow an initial attack on Suh's "reckless remarks" Sunday, in which she warned the South should "discipline itself if it wants to stave off disaster".

North Korea had paused its long-range and nuclear tests when Kim Jong Un and then US president Donald Trump engaged in a high-profile bout of diplomacy that subsequently collapsed in 2019. Talks have since stalled.

North Korea will this month mark the 110th anniversary of the birth of founder Kim Il Sung -- the grandfather of current leader Kim.

Typically, Pyongyang likes to mark key domestic anniversaries with military parades, major weapons tests or satellite launches.