SEOUL - The leaders of the United States, Japan and South Korea have agreed that boosting trilateral cooperation is crucial in resolving issues in the region, including the growing threat posed by North Korea's expanding nuclear and missile capability.

They have also stressed the need to increase trilateral security cooperation and strengthen America's extended deterrence for its two allies.

US President Joe Biden met Japanese Prime Minister Fumio Kishida and South Korean President Yoon Suk-yeol on the sidelines of the Nato summit held in Madrid on Wednesday (June 29).

It was the first trilateral summit in five years and the first time the trio were gathered in an effort to rebuild ties.

Their predecessors had met in New York during the last summit in 2017, after which Washington neglected diplomacy as a rift grew between Tokyo and Seoul due to a dispute over wartime forced labour.

President Yoon, who was inaugurated in May, has voiced intentions to align more closely with the US and mend ties with Japan.

On Wednesday, he stressed the "urgent need" for Washington, Tokyo and Seoul to jointly respond to Pyongyang's growing provocations, according to a statement from his office.

The regime has conducted at least 18 rounds of missile tests since January and is expected to carry out its seventh nuclear test any time.

"North Korea's nuclear and missile threats continue to evolve, and the global landscape is facing increased uncertainties, thereby rendering our trilateral partnership all the more significant," Mr Yoon said in his opening remarks, according to a White House transcript.

"I hope that our meeting will position our partnership as yet another central pillar for global peace and stability."

President Biden underscored America's "unshakable commitment" to the defence of both Japan and South Korea, while stressing that trilateral cooperation is "essential to achieving our shared objective, including a complete denuclearisation of the Korean peninsula and a free and open Indo-Pacific".

He also expressed deep concern over North Korea's escalatory missile tests and potential nuclear test.

Mr Kishida voiced hope that the three nations can respond to the anticipated nuclear test "at the trilateral level, including joint exercises".

They also agreed to work closely to bring North Korea back to the dialogue table.

Negotiations have stalled since 2019 when talks between North Korean leader Kim Jong Un and former US president Donald Trump broke down due to differences over sanctions relief and denuclearisation steps.

Separately, President Yoon voiced hopes to improve ties with Japan when he met Mr Kishida during an earlier gala dinner hosted by Spanish King Felipe VI.

Mr Yoon was cited by his office as telling Mr Kishida that he plans to "resolve pending issues between South Korea and Japan as early as possible and move forward in a future-oriented manner".

The Japanese Premier responded by saying he hoped to work with Mr Yoon to develop "healthier" bilateral ties.

While in Madrid, the duo also joined Nato's Asia-Pacific Partners summit with their counterparts from Australia and New Zealand.

The four leaders pledged to continue working closely for the peace and stability of the Indo-Pacific region, according to a statement from Japan's Ministry of Foreign Affairs.

They were also unanimous in condemning Russia's invasion of Ukraine.

Mr Kishida, who hosted the meeting, said that the invasion shook the very foundations of the global order and that unilateral changes of the status quo by force cannot be allowed anywhere in the world.

• Additional reporting by Charissa Yong in Washington, Walter Sim in Tokyo