North Korean leader Kim Jong Un vowed to deal a "death blow" to his country's enemies, state media said Thursday, as South Korea's hawkish ruling party suffered a defeat in parliamentary elections.

So far this year, the nuclear-armed North has declared South Korea its "principal enemy", jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.

If provoked, North Korea will "deal a death-blow to the enemy without hesitation by mobilising all means in its possession", Kim said, according to Pyongyang's official Korean Central News Agency (KCNA).

He made the remarks during a visit to the Kim Jong Il University of Military and Politics on April 10, the same day as South Korea's parliamentary election, KCNA said.

"Now is the time to be more thoroughly prepared for a war than ever before," Kim said.

North Korea "should be more firmly and perfectly prepared for a war, which should be won without fail, not just for a possible war."

Partially blurred images released by state media depicted Kim, surrounded by army officials, inspecting what appeared to be a miniature of South Korea's capital Seoul, including its Han River, along with maps of the peninsula.

South Korea's parliamentary election result handed a defeat to the party of incumbent President Yoon Suk Yeol, who has taken a tough line with the nuclear-armed North while improving ties with Washington.

It also makes him a likely lame duck for his remaining three years in office.

The main opposition Democratic Party, which won by a landslide, favours a softer approach towards Pyongyang.

The result is good news for Kim, especially with the prospect of the return of former US President Donald Trump in November elections, analysts say.

Experts speculate that Trump, who had historic but ultimately unsuccessful summits with Kim during his presidency, may favour engagement with Pyongyang should he return to the White House.

Kim has recently bolstered military ties with Russia, which last month used its veto power at the UN Security Council to effectively end UN expert monitoring of North Korean sanctions violations.