North Korea’s foreign ministry said on Tuesday that it will keep bolstering its nuclear force, denouncing a recent joint pledge by the United States, South Korea and Japan for its denuclearisation, according to state media KCNA.

US Secretary of State Marco Rubio, South Korean Foreign Minister Cho Tae-yul and Japanese Foreign Minister Iwaya Takeshi held talks on Saturday on the sidelines of a security conference in Munich and issued a statement reaffirming their commitment to North Korea's complete denuclearisation.

Pyongyang’s foreign ministry criticised the countries for pursuing an “outdated, absurd” plan, warning against seeking what it called “foolish acts inciting collective hostility and conflicts.”

“As long as the US and its vassal forces’ hostile threat exists, the DPRK’s nukes are means for defending peace and sovereignty and a means for legitimate self-defence entrusted by the constitution of the state,” an unnamed ministry spokesperson said in a statement carried by KCNA, vowing to continue strengthening its nuclear force.

The spokesperson was referring to North Korea’s formal name, the Democratic People’s Republic of Korea.

South Korea’s foreign ministry urged the North to cease its illicit weapons programmes and return to the path to denuclearisation.

“North Korea will never be recognised as a nuclear weapons state,” ministry spokesperson Lee Jae-woong told a briefing. “We hope that they will realise that the development of nuclear weapons and missiles will only hinder their own security and economic development.”

The three-way meeting was their first since the inauguration of US President Donald Trump, who held unprecedented summits with North Korean leader Kim Jong Un during his first term and has touted their personal rapport.

South Korean lawmakers, after being briefed by the National Intelligence Service, have said that Pyongyang’s recent missile tests were in part intended to “show off its US deterrent assets and drawing Trump’s attention.”

Also in Seoul, South Korea’s military said on Tuesday it has deployed a domestically developed new bunker buster missile named the Korean Tactical Surface to Surface Missile (KTSSM).

The missile - nicknamed Ure, which means thunder in Korean - is capable of conducting simultaneous, precision strikes in a short span of time against North Korea’s long-range artillery systems that could threaten the greater Seoul area in the event of a contingency, the military said in a press release.