Officials from the United States and its Asian allies, Japan and South Korea, suspect North Korea is preparing for a nuclear test, and vice foreign ministers from the three countries said on Wednesday that their joint response would be “decisive”.

Cho Hyundong, South Korea’s first vice foreign minister, said the trio are bolstering their defence co-operation to deter the growing possibility of North Korea’s use of nuclear weapons since the adoption in September of legislation spelling out scenarios where it would use them, including pre-emptively.

North Korea’s new nuclear policy is “creating a serious tension on the Korean Peninsula”, Mr Cho told a joint news conference after talks in Tokyo with US deputy secretary of state Wendy Sherman and Japanese vice foreign minister Takeo Mori.

“South Korea and the US will step up their extended deterrence by utilising all the elements of the national power and show an overwhelming, decisive response to any use of a nuclear weapon by North Korea,” he said.

In 2022 alone, North Korea has launched more than 20 ballistic missiles at unprecedented pace, including one that flew over northern Japan in early October.

It has also fired a barrage of artillery towards the south in response to South Korea’s joint military exercises with the US, which Pyongyang views as a practice to invade the country.

Ms Sherman, during a meeting with Mr Cho on Tuesday ahead of the three-way talks, criticised North Korea’s military actions as “irresponsible, dangerous and destabilising”, and said the US will fully use its military capabilities, including nuclear, as she warned North Korea against escalating its provocations.

She stressed again on Wednesday that the co-operation between the three countries is “ironclad”, citing signs of Japan and South Korea improving their troubled ties over historical wartime-related disputes.

“There is so much we can achieve and are achieving when our countries work together,” she said.

It was the second in-person meeting of the three officials since conservative South Korean President Yoon Suk Yeol took office in May, signalling an improvement in difficult ties between Tokyo and Seoul.

A year ago in Washington, Japanese and South Korean vice ministers declined to participate in a joint news conference after their talks, leaving Ms Sherman to make a solo media appearance.

The three officials also condemned Russia’s nuclear threat, as well as any other escalation of threats, and its unsubstantiated allegation that Ukraine is preparing to launch a so-called dirty bomb – which uses explosives to scatter radioactive waste – as unacceptable.

Mr Mori said the three officials also agreed to closely watch China’s maritime activity in the East and South China Seas and the situation in the Taiwan Strait under Chinese President Xi Jinping’s third term.