A second US submarine arrived in South Korea on Monday, following the recent deployment of the first US nuclear-armed submarine in the country in four decades.

The USS Annapolis docked at a naval base on South Korea's southern island of Jeju to load military supplies as part of an unspecified operational mission, the South Korean navy said.

The move is seen as a part of the two allies joint effort to counter North Korea's nuclear threats.

North Korea issues threats

Earlier, the USS Kentucky had arrived at a port in Busan on the mainland about a week ago.

North Korea responded to the arrival of the USS Kentucky with the test-firing of ballistic and cruise missiles.

The defense minister of North Korea even made veiled threats, suggesting the possibility of using a nuclear weapon in response to the submarine's docking.

First US nuclear-armed sub visit since 1980s

The USS Annapolis, while powered by a nuclear reactor, is not nuclear-armed and is equipped with conventional weapons. Its primary mission is to destroy enemy ships and submarines.

In September last year, the USS Annapolis had participated in trilateral anti-submarine exercises with South Korea and Japan in international waters off the Korean Peninsula.

The USS Kentucky's docking in South Korea the previous week marked the first visit of a US nuclear-armed ballistic missile submarine to South Korea since the 1980s. It coincided with talks between the US and South Korea aimed at coordinating responses in the event of a nuclear conflict with North Korea.

ss/fb (AP, Reuters)