US and South Korea sign nuclear weapons deal

US President Joe Biden and South Korean President Yoon Suk-yeol have secured a landmark deal which includes plans to periodically deploy US nuclear-armed submarines in South Korea.

Washington has also agreed to involve Seoul in its planning for any use of nuclear weapons against North Korea.

In return, South Korea has agreed to not develop its own nuclear weapons.

The deal, called the Washington Declaration, will strengthen the allies' co-operation in deterring a North Korean attack, Mr Biden said.

He spoke on Wednesday during a joint press conference with Mr Yoon, who is in Washington this week to discuss issues including the war in Ukraine, climate change, cyber co-operation and nuclear power.

The South Korean leader said the Washington Declaration - the centrepiece of this week's state visit - marked an "unprecedented" step to enhance extended deterrence, a commitment from the US to deter attacks and protect US allies using its military power, including nuclear weapons.

The declaration comes amid rising concerns about nuclear threats from North Korea as the country carries out a record number of ballistic missile tests.

"It's about strengthening deterrence in response to the DPRK's [North Korea's] escalatory behaviour," Mr Biden said.

The new agreement is a result of negotiations that took place over the course of several months, senior administration officials told reporters this week.

Under the deal, the US will aim to take steps to "make its deterrence more visible through the regular deployment of strategic assets, including a US nuclear ballistic submarine visit to South Korea, which has not happened since the early 1980s", officials told reporters this week.

The two sides will also develop a Nuclear Consultative Group to discuss nuclear and strategic planning issues.

Politicians in Seoul have long been pushing Washington to involve them more in planning for how and when to use nuclear weapons against North Korea.

As North Korea's nuclear arsenal has grown in size and sophistication, South Koreans have grown wary of being kept in the dark over what would trigger Mr Biden to push the nuclear button on their behalf. A fear that Washington might abandon Seoul has led to calls for South Korea to develop its own nuclear weapons.

But in January, Mr Yoon alarmed policymakers in Washington when he became the first South Korean president to put this idea back on the table in decades.

It suddenly became clear to the US that reassuring words and gestures would no longer work, and if it was to dissuade South Korea from wanting to build its own bombs, it would have to offer something concrete.

Furthermore, Mr Yoon had made it clear that he expected to return home having made "tangible" progress.

This new Nuclear Consultative Group ticks the box, providing the increased involvement the South Korean government has been asking for, but the bigger question is whether it will quell the public's anxieties.

It does not ink a total commitment from the US that it would use nuclear weapons to defend South Korea if North Korea were to attack.

However on Wednesday Mr Biden said: "A nuclear attack by North Korea against the United States or its allies and partners is unacceptable and will result in the end of whatever regime were to take such an action".

Plans for a nuclear-armed submarine to visit South Korea for the first time in four decades adds further weight to the US commitment.

In return, the US has demanded that South Korea remain a non-nuclear state and a faithful advocate of the non-proliferation of nuclear weapons. The US sees dissuading South Korea from going nuclear as essential, fearful that if it fails, other countries may follow in its footsteps.

But it is unclear how this commitment will be received by the influential, and increasingly vocal, group of academics, scientists and members of South Korea's ruling party who have been pushing for Seoul to arm itself.