The test was by far the most significant since Pyongyang first began a dialogue with Washington in 2018 over pressure to give up its nuclear weapons. Analysts said the new capability marks a significant step in strengthening that programme.

“We assess that it was a short- to medium-range ballistic missile. And I would say that we have no indication that it was launched from a submarine but rather a sea-based platform,” a US military spokesman, Colonel Pat Ryder, told reporters.

Meanwhile, the United Nations Security Council is expected to hold closed-door talks early next week on the latest test, diplomats said. The talks were requested by Britain, France and Germany, as the European powers push for the world body to keep up pressure on Pyongyang. North Korea is banned from ballistic missile launches by Security Council resolutions.

Trump has said he has no problem with a string of short-range rocket tests conducted by North Korea, calling them “normal”.

But a proven submarine-based missile capability would take the North’s arsenal to a new level, allowing deployment far beyond the Korean peninsula and a second-strike capability in the event of an attack on its military bases.

“The new-type ballistic missile was fired in vertical mode” on Wednesday in the waters off Wonsan Bay, the Korean Central News Agency (KCNA) reported, identifying the weapon as a Pukguksong-3.

“The successful new-type SLBM test-firing comes to be of great significance as it ushered in a new phase in containing the outside forces’ threat,” it added.

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The North’s leader, Kim Jong-un, sent “warm congratulations” to research units involved in the launch. Kim has personally supervised recent land-based missile tests.

Photos carried by the official Rodong Sinmun newspaper showed a black and white missile emerging from the water and appearing to shoot into the sky.

The images also showed a small towing vessel next to the missile, which analysts said indicated that the test was conducted from a submersible barge rather than an actual submarine, and that the system was in its early stages.

Ankit Panda of the Federation of American Scientists called it Pyongyang’s longest-range-capable solid-fuel missile, adding that Wednesday’s launch was “unambiguously the first nuclear-capable missile test since November 2017”.

“Kim Jong-un’s ‘rocket men’ kept busy during the diplomatic charm offensives of 2018-2019,” Panda said.

The North carried out a successful test of the solid-fuel Pukguksong-1, also known as KN-11, in August 2016, which flew around 500km (300 miles).

In July, North Korean state media had published pictures of Kim inspecting a new type of submarine that also showed a poster of the Pukguksong-3 on a wall, fuelling concerns that Pyongyang was pushing ahead with an SLBM programme.

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Tokyo said a part of Wednesday’s missile landed in waters within Japan’s exclusive economic zone – a 200km (125-mile) band around Japanese territory.

Washington voiced alarm, with a State Department spokesperson calling on Pyongyang “to refrain from provocations” and “remain engaged in substantive and sustained negotiations” aimed at bringing stability and denuclearisation.

The launch came ahead of planned resumption of working-level talks between Pyongyang and Washington, which are slated for later this week in an undisclosed location.

A delegation headed by North Korea’s chief nuclear negotiator Kim Myong-gil has landed in Stockholm, Sweden, for denuclearisation talks with the US, a source familiar with the matter said on Thursday.

Earlier on Thursday Kim, speaking to Yonhap news agency at Beijing airport, said he and other officials were heading to Sweden.

“We’re going for the DPRK-US working-level negotiations,” Kim told reporters in Beijing, according to Yonhap. “There’s been a new signal from the US side, so we’re going with great expectations and optimism about the outcome.”

North Korea frequently couples diplomatic overtures with military moves as a way of maintaining pressure on negotiating partners, analysts say, and may believe this weapons system gives it added leverage.

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Pyongyang tested what it called a “super-large” rocket launcher last month just hours after the North said it was willing to resume working-level talks with Washington.

Kim Dong-yub, a researcher at the Institute for Far Eastern Studies, noted the North Korean leader’s absence at Wednesday’s launch – a rarity as he has been present at all recent weapons tests.

“It’s likely not unrelated to the talks between Pyongyang and Washington currently under way,” he said, adding that Kim Jong-un was trying to carry out weapons modernisation without jeopardising dialogue with the US.

Negotiations have been deadlocked since a second summit between Kim and Trump in February ended without a deal.

The two agreed to restart dialogue during an impromptu meeting at the demilitarised zone dividing the two Koreas in June, but those talks have yet to materialise.

Pyongyang also carried out several weapons tests since the meeting that have been downplayed by Trump, who dismissed them as “small” and insisted his personal ties with Kim remained good.

Additional reporting by Reuters