North Korea has said it test launched ballistic missiles from a train in what was seen as an apparent retaliation against fresh sanctions imposed by the US.

The report by state media came a day after South Korea’s military said it detected the North firing two missiles into the sea in its third weapons launch this month.

The launch came hours after Pyongyang’s Foreign Ministry issued a statement berating the US for imposing new sanctions over the North’s previous tests and warned of stronger and more explicit action if Washington maintains its “confrontational stance”.

North Korea in recent months has been ramping up tests of new missiles designed to overwhelm missile defences in the region amid pandemic-related border closures and a freeze in nuclear diplomacy with the US.

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A missile test from a railway in North Pyongan Province (Korean Central News Agency/Korea News Service/AP)

Some experts say North Korean leader Kim Jong Un is going back to a tested technique of pressuring the US and neighbours with missile launches and threats before offering negotiations meant to extract concessions.

North Korea’s official Korean Central News Agency said Friday’s exercise was aimed at checking the alert posture of its army’s rail-borne missile regiment.

The troops swiftly moved to the launch site after receiving the missile-test order on short notice and fired two “tactical guided” missiles that accurately struck a sea target, the report said.

The North’s Rodong Sinmun newspaper published photos of what appeared to be two different missiles soaring above from railway carriages engulfed in smoke.

Cheong Seong-Chang, an analyst at the private Sejong Institute in South Korea, said the North is likely to have staged a launch that had not been previously planned to demonstrate its opposition to US sanctions.

The missiles appeared to be a solid-fuel short-range weapon the North has apparently modelled after Russia’s Iskander mobile ballistic system.

First tested in 2019, the missile is designed to be manoeuvrable and fly at low altitudes, which potentially improve its chances of evading and defeating missile systems.

The North first launched the missiles from a train in September as part of efforts to diversify its launch options, which now includes various vehicles and may eventually include submarines, depending on the country’s progress.

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A missile test by the North Korean government (Korean Central News Agency/Korea News Service/AP)

Firing a missile from a train could add mobility, but some experts say North Korea’s simple rail networks running through its relatively small territory would be quickly destroyed by enemies during a crisis.

The Biden administration on Wednesday imposed sanctions on five North Koreans over their roles in obtaining equipment and technology for the North’s missile programmes in its response to the previous tests this month.

The announcement by the Treasury Department came hours after Pyongyang said Mr Kim had overseen a successful test of a hypersonic missile on Tuesday that he claimed would greatly increase the country’s nuclear “war deterrent”.

Tuesday’s test was North Korea’s second demonstration of its purported hypersonic missile in a week.

Experts say North Korea would need years and more successful and longer-range tests before achieving a credible hypersonic system.

A US-led diplomatic push aimed at convincing Pyongyang to abandon its nuclear weapons programme collapsed in 2019 after the Trump administration rejected the North’s demands for major sanctions relief in exchange for a partial surrender of its nuclear capabilities.

Mr Kim has since pledged to further expand a nuclear arsenal he clearly sees as his strongest guarantee of survival, despite the country’s economy suffering major setbacks amid pandemic-related border closures and persistent US-led sanctions.

His government has so far rejected the Biden administration’s call to resume dialogue without preconditions, saying the US must first abandon its “hostile policy”.