North Korea says US carrier's visit to South 'undisguised' provocation

North Korea denounced on Friday a US aircraft carrier's visit to South Korea, calling it a provocation that could bring "irrevocable, catastrophic circumstances".

The nuclear-powered Ronald Reagan and its strike group arrived in the South Korean port of Busan on Thursday for a five-day visit, after allied exercises in nearby waters, in a show of force against North Korea.

The aircraft carrier's visit showed that a US scheme for a nuclear attack on North Korea had reached "the most serious phase", North Korea's official KCNA news agency said, adding this meant "the outbreak of a nuclear war comes to the fore".

"It is an undisguised military provocation driving the situation to irrevocable catastrophic circumstances," KCNA said in a commentary.

US and South Korean forces have been staging intensified military exercises this year, involving US aircraft carriers, submarines and advanced bombers, in order, they say, to better respond to evolving North Korean nuclear and missile threats.

North Korea calls the drills a rehearsal for invasion.

Seth Koenig, a spokesman for the carrier strike group, said it frequently visits South Korea providing "opportunities to build interoperability at sea together towards shared goals of a free and open Indo Pacific".

The North Korean news agency said that in case of an imminent nuclear attack, North Korea would take "necessary action", as enshrined in its nuclear doctrine, to "thoroughly deter and repel" a move to "ignite a nuclear war".

Our "most powerful and rapid first strike will be given to the 'extended deterrence' means, used by the US to hallucinate its followers, and the bases of evil in the Korean peninsula and its vicinity," KCNA said.

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

US, Japanese and South Korean nuclear envoys will hold two days of talks from Monday in the Indonesian capital to discuss North Korea, the Japanese and South Korean foreign ministries said.

Japan has regularly participated in air and naval exercises with the allies.