North Korea has stipulated the policy of strengthening its nuclear force in the constitution at a key parliamentary meeting, as leader Kim Jong-un said trilateral security cooperation between South Korea, the United States, and Japan poses "the worst actual threat."

The decision was made at the ninth session of the 14th Supreme People's Assembly (SPA) held on Tuesday and Wednesday, with leader Kim's attendance, according to the North's official Korean Central News Agency (KCNA).

At the session, the North unanimously decided to "supplement Article 58 of Chapter 4 of the Socialist Constitution" to ensure the country's right to existence and development, deter war and protect regional and global peace by rapidly developing nuclear weapons to a higher level, Kim said.

"The DPRK's nuclear force-building policy has been made permanent as the basic law of the state, which no one is allowed to flout with anything. This is a historic event that provided a powerful political lever for remarkably strengthening the national defense capabilities," he said in a speech at the session, using the acronym of North Korea's official name.

At an SPA meeting in September last year, North Korea enacted a new nuclear law authorizing the preemptive use of nuclear arms, calling its status of a nuclear state "irreversible."

In the speech, Kim said the establishment of what he called the "triangular military alliance" between the US, South Korea, and Japan "finally resulted in the emergence of the 'Asian-version NATO,' the root cause of war and aggression."

"This is just the worst actual threat, not threatening rhetoric or an imaginary entity," he said.

Under a state policy to "physically remove" the North, Kim said the US also has "maximized its nuclear war threats by "resuming the large-scale nuclear war joint drills with clear aggressive nature and putting the deployment of its strategic nuclear assets near the Korean peninsula on a permanent basis."

He also said that the "Nuclear Consultative Group" between the US and South Korea is aimed at using nuclear weapons against the North. The NCG was established when Presidents Yoon Suk Yeol and Joe Biden held a summit in April. It is designed to discuss nuclear and strategic planning issues.

Kim also stressed the need to "exponentially" bolster the country's nuclear arsenal and diversify its nuclear strike capability as well as deployment with different branches and units of the armed forces.

Kim also vowed to strengthen solidarity with countries standing against the US.

His message came as North Korea has been seeking to bolster its ties with China and Russia vis-a-vis the strengthening of security cooperation among Seoul, Washington and Tokyo.

Joined by Russia's visiting defense minister and a senior Chinese official, the North's leader oversaw a military parade to mark its key anniversary in late July, a scene seen as intended to display solidarity among the three nations.

Earlier this month, Kim also traveled to Russia on his armored train for talks with Vladimir Putin amid concerns about a possible arms deal between the two nations.

The SPA is the highest organ of state power under the North's constitution, but it actually only rubber-stamps decisions by the ruling Workers' Party of Korea (WPK).

At the latest session, North Korea did not dismiss Premier Kim Tok-hun despite speculation that the North's leader may replace him over the poor response to flooding and storm damage from Tropical Storm Khanun in August.

The North Korean leader has strongly berated the premier and the Cabinet over their "irresponsible" attitude in failing to prevent flood damage and "spoiling" the country's economic plans.

However, Premier Kim has continued with his official duties, including an inspection of the agricultural sector in a provincial area, raising the possibility that he may remain in office.

At the SPA meeting, North Korea also renamed the National Aerospace Development Administration, an agency in charge of launching military spy satellites, to the National Aerospace Technology General Bureau.

The secretive regime earlier announced a plan to make a third attempt to launch a military spy satellite in October following its two failed attempts in May and August. (Yonhap)