North Korea fires missiles off its coast as US nuclear sub arrives in South Korea

US military officials said the missiles posed no threat to US forces, territories or its allies

North Korea fired two ballistic missiles into the sea off its east coast on Monday, according to South Korea's military. The launch appears to be a reaction to a US nuclear-powered submarine's recent arrival at a South Korean military base.

The reports were corroborated by Japan's defence ministry, which also detected a launch of what it said could be a ballistic missile by North Korea. Japanese media reports citing a government source claimed that the nation may have launched multiple missiles.

The missile launch is the latest incident during a period of high tension on the Korean peninsula. The US and South Korea are increasing their military readiness against North Korea's weapons programmes, which includes an increase in US military assets in the region, according to Reuters.

Pyongyang reacted to the ramp-up by claiming that the US and South Korea’s actions may meet its standards to justify the use of nuclear weapons.

US officials said they were in close contact with allies concerning the missile launches. On Monday US military officials said the launches posed no immediate threats to US personnel and territory or to US allies, though they did say the launches were a destabilising force in the region.

The US sub arrived at a South Korea naval base on the southern island of Jeju on Monday, where it was scheduled to collect military supplies on an unspecified operational mission, according to a statement from the South Korean navy.

This is the second time in the last seven days that North Korea has fired off missiles. It shot another barrage of missiles into the sea off its west coast over the weekend. The nation also conducted ballistic missile tests last week after a US nuclear-armed sub arrived at a South Korean port for the first time since the 1980's.

The launches come as US officials are attempting to negotiate the release of Travis King from North Korean custody. Mr King is a US Army private who fled across the border after spending 47 days in detainment in South Korea for alleged assault and destruction of property.