North Korean leader Kim Jong Un has clearly displayed a confrontational attitude toward the United States, state-run media said Saturday ahead of U.S. President-elect Joe Biden's inauguration on Jan. 20, describing Washington as Pyongyang's "biggest enemy."

At the first congress of the ruling party in nearly five years, which started Tuesday, Kim also pledged to further strengthen the country's nuclear arsenal while saying the United States will not change its hardline stance against North Korea, whoever is president.

It was Kim's first direct mention of Pyongyang's ties with Washington since the U.S. presidential election in November, where Democrat Biden defeated incumbent Republican Donald Trump.

North Korean leader Kim Jong Un is pictured at the congress of the Workers' Party in Pyongyang on Jan. 6, 2021. (KCNA/Kyodo)

North Korea should "subdue the United States, the biggest enemy that is a basic obstacle to the development" of the nation's revolution, Kim was quoted by the official Korean Central News Agency as saying at the rare meeting of the Workers' Party.

"No matter who is in power in the United States, the substance of the United States and the true spirit of its fundamental policy toward North Korea will never change," Kim said.

To establish a "new relationship" between the two countries, the United States would have to abandon its "hostile" policy toward North Korea, Kim said, adding Pyongyang will not use nuclear weapons unless hostile forces try to utilize them against it.

Regarding inter-Korean ties, Kim said the North has "no need to unilaterally provide goodwill toward the South at this juncture," calling on Seoul to stop any hostile action.

The Korean Peninsula has been divided since the 1950-1953 Korean War ended in a cease-fire. Washington, which fought alongside Seoul, technically remains in a state of war with Pyongyang.

KCNA said the congress will continue in session. Speculation had grown that the gathering would be wrapped up on Friday, Kim's presumed birthday, but the news agency did not elaborate on when it will conclude.

The previous party congress, the first in 36 years, was held for four days from May 6, 2016.

After the last congress, Kim accelerated the development of nuclear weapons and ballistic missiles, including those that could reach the U.S. mainland. In November 2017, he declared the completion of a "state nuclear force."

Starting in June 2018, Kim held meetings with Trump three times, but their denuclearization negotiations were at a standstill, making it more difficult for Pyongyang to persuade Washington to lift economic sanctions.

At home, North Korea's economy has become more sluggish after cutting off traffic to and from its neighbors since early last year to prevent the novel coronavirus, first detected in the Chinese city of Wuhan, from entering the nation.

With trade with China, North Korea's closest and most influential ally, plunging and powerful typhoons and flooding devastating the agricultural sector, concerns have been mounting that its citizens are not receiving adequate daily necessities.

China's trade with North Korea plummeted to its lowest level for a second straight month in November, the latest data showed. North Korea has depended on China for more than 90 percent of its trade.

At the opening of the ruling party gathering, Kim said in a speech that North Korea failed to achieve the economic development goals set in its strategy through 2020 in almost all sectors.

North Korea is believed to be vulnerable to infectious diseases against a backdrop of chronic shortages of food and medical supplies triggered by economic sanctions aimed at thwarting its nuclear and ballistic missile ambitions.

In the past, North Korea barred foreigners from entering the country during the 2003 epidemic of severe acute respiratory syndrome, or SARS, and the Ebola outbreak in West Africa in 2014.

Pyongyang claims the virus that causes COVID-19 disease has not made inroads into the nation, but many diplomats and international organization officials in the country's capital have left North Korea since March 2020.