South Korea, U.S. discussing nuclear exercises as tensions flare with North - Yoon

South Korea and the United States are discussing possible joint planning and exercises using US nuclear assets in the face of North Korea's growing nuclear and missile threats, South Korean President Yoon Suk-yeol said in a newspaper interview.

The Chosun Ilbo newspaper quoted Yoon as saying the joint planning and exercises would be aimed at a more effective implementation of the US "extended deterrence."

The term means the ability of the US military, particularly its nuclear forces, to deter attacks on US allies.

"The nuclear weapons belong to the United States, but planning, information sharing, exercises and training should be jointly conducted by South Korea and the United States," Yoon said, adding Washington is also "quite positive" about the idea.

Yoon's remarks come a day after North Korean state media reported that its leader Kim Jong Un called for developing new intercontinental ballistic missiles (ICBMs) and an "exponential increase" of the country's nuclear arsenal to counter US-led threats amid flaring tension between the rival Koreas.

The North's race to advance its nuclear and missile programmes has renewed debate over South Korea's own nuclear armaments, but Yoon said maintaining the Treaty on the Non-Proliferation of Nuclear Weapons remained important.

At a meeting of the ruling Workers' Party last week, Kim said South Korea has now become the North's "undoubted enemy" and rolled out new military goals, hinting at another year of intensive weapons tests and tension.

Inter-Korean ties have long been testy but have been even more frayed since Yoon took office in May.

On Sunday, North Korea fired a short-range ballistic missile off its east coast, in a rare late-night, New Year's Day weapons test, following three ballistic missiles launched on Saturday, capping a year marked by a record number of missile tests.

Yoon's comments on the nuclear exercises are the latest demonstration of his tough stance on North Korea. He urged the military to prepare for a war with "overwhelming" capability following North Korean drones crossing into the South last week.

Analysts say the tensions could worsen.

"This year could be a year of crisis with military tension on the Korean peninsula going beyond what it was like in 2017," said Hong Min, a senior researcher at the Korea Institute for National Unification, referring to the days of the "fire and fury" under the Trump administration.

"North Korea's hardline stance...and aggressive weapons development when met with South Korea-US joint exercises and proportional response could raise the tension in a flash, and we cannot rule out what's similar to a regional conflict when the two sides have a misunderstanding of the situation," Hong said.