North Korea has threatened its southern neighbor with nuclear fire, following the stopover of an American nuclear submarine on Thursday July 20. This new threat comes against amid growing cooperation between Seoul and Washington over Pyongyang’s expanding nuclear program.

North Korea’s defence minister said Thursday the current port visit of a US nuclear-capable submarine to South Korea could meet the legal conditions under which Pyongyang would use its nuclear weapons.

Relations between the two Koreas are at one of their lowest points ever, with diplomacy stalled and North Korean leader Kim Jong Un calling for increased weapons development, including tactical nuclear weapons.

The United States and South Korea have stepped up displays of military muscle in response, and a US nuclear-capable submarine made a port call to South Korea this week for the first time since 1981.

Pyongyang’s defence minister Kang Sun Nam said the arrival in Busan port of a US Ohio-class submarine “may fall under the conditions of the use of nuclear weapons specified in the DPRK law on the nuclear force policy”, referring to North Korea by its official name.

North Korea last year adopted a sweeping nuclear law, setting out an array of scenarios in which it could use its nukes, including pre-emptive nuclear strikes if threatened.

Ohio-class subs can carry up to 20 Trident II ballistic missiles. The US Navy typically does not confirm if a submarine is carrying nuclear weapons before it goes out to sea.

North Korea has conducted a string of banned weapons tests this year, including twice launching its newest solid fuel Hwasong-18 intercontinental ballistic missile.

Seoul and Washington have ramped up defence cooperation in response, staging joint military exercises with advanced stealth jets and US strategic assets.

Washington first announced it would deploy a submarine capable of launching ballistic missiles with nuclear warheads to the Korean peninsula in April, while Yoon was on a state visit.

North Korea baulks at having US nuclear assets deployed around the Korean peninsula.

Malo Pinatel, with AFP