North Korea also claimed US reconnaissance planes recently violated its air space near the east coast, quoting an unnamed spokesperson of its national defence ministry in a statement carried by the official KCNA news agency.

“There is no guarantee that a shocking incident where a US air force strategic reconnaissance plane is shot down over the East Sea will not happen,” the spokesman said.

The moves by the US to introduce strategic nuclear assets to the Korean peninsula is a blatant nuclear blackmail against North Korea and regional countries and presents a grave threat to peace, KCNA said.

A US nuclear-powered cruise missile submarine arrived at the port of Busan in South Korea last month.

In April, the leaders of South Korea and the US agreed a US Navy nuclear-armed ballistic missile submarine will visit South Korea for the first time since the 1980s but no timetable has been given for such a visit.