Pyongyang, North Korea – North Korea's ruler Kim Jong-un has reiterated his call for an expansion of the isolated country's nuclear capabilities at the close of the ruling Workers' Party's 8th congress.

"While further strengthening our nuclear war deterrent, we need to do everything to build the strongest military capabilities," Kim told the party congress, South Korea's news agency Yonhap reported, citing North Korean state media.

"By accelerating the push to make our military more elite and strong, we need to have them thoroughly prepared to play their role against any form of threats or unexpected situations," Kim added.

At the same time, on the last day of the congress in the capital Pyongyang, Kim declared that the country must also concentrate on developing the economy and improving people's living conditions.

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The rare party congress was held shortly before the inauguration of US president-elect Joe Biden in Washington DC next week, at a time when the negotiations with the United States over North Korea's disputed nuclear ambitions are at a standstill.

On Friday, Kim had called for an expansion of North Korea's nuclear capabilities and called the United States its "biggest enemy."

North Korea remains internationally isolated because of its nuclear weapons program.

At the start of the party congress, Kim admitted on Tuesday that the goals of the old five-year plan for economic development drawn up in 2016 had not been met.

The congress, which was originally supposed to be held every five years, is formally the party's most important body. However, the seventh congress in May 2016 was the first in 36 years.