The display came after the five-yearly congress of the ruling Workers' Party, where leader Kim Jong Un decried the US as his country's "foremost principal enemy".

A grinning Kim oversaw the parade on Thursday evening, wearing a black leather coat and fur hat as he watched infantry troops, artillery, tanks, and a flypast with aircraft forming the number "8" to commemorate the party meeting.

"The world's most powerful weapon, submarine-launch ballistic missile, entered the square one after another, powerfully demonstrating the might of the revolutionary armed forces," the official KCNA news agency said.

Pictures showed at least four of the SLBMs with black-and-white cones being driven past flag-waving crowds in Kim Il Sung Square, and Park Won-gon of Handong Global University in the South described them as "the North's ultimate nuclear weapon".

The North has shown off earlier, smaller SLBMs before, and broadcast footage of a test launch, but it was not clear whether that missile was fired from a submarine or an underwater platform.

A working SLBM on a nuclear-powered submarine would be a strategic game-changer, enabling Pyongyang to launch a surprise attack from close to the United States or carry out a strike even if its land-based forces had been destroyed.

At the congress, Kim said the North had completed plans for a nuclear submarine, but any such vessel is likely to be years away from going into service.

Analysts say the North is using the party meeting and military display to send the incoming administration in Washington a carefully calibrated message of strength in an attempt to extract concessions.

KCNA said the parade included rockets with a "powerful striking capability for thoroughly annihilating enemies in a preemptive way outside the territory" -- implying a range extending beyond the Korean peninsula.

Images showed the display culminating with what appeared to be a new solid-fuel short-range ballistic missile -- which are more mobile and more quickly deployed than liquid-fuelled versions.

"They'd like us to notice that they're getting more proficient with larger solid rocket boosters," tweeted Ankit Panda of the Carnegie Endowment.

But Pyongyang did not appear to put on show any of its intercontinental ballistic missiles (ICBMs), unlike at its previous parade in October, when it revealed a huge new ICBM on an 11-axle vehicle that analysts said was the largest road-mobile, liquid-fuelled missile in the world.

"The majestic elite units and invincible iron-clad ranks of the Republic which will proudly pass Kim Il Sung Square represent our absolute power," North Korean defence minister Kim Jong Gwan said in a speech ahead of the Thursday evening parade, KCNA reported.

- 'Well-calculated' -

Kim and Donald Trump had a tumultuous relationship, engaging in mutual insults and threats of war before an extraordinary diplomatic bromance featuring headline-grabbing summits and declarations of love by the outgoing US president.

But little substantive progress was made, with the process deadlocked after a February 2019 summit in Hanoi broke down over sanctions relief and what Pyongyang would be willing to give up in return.

The North is under multiple sets of international sanctions over its banned nuclear weapons and ballistic missile programmes, which have made rapid progress under Kim and which it says it needs to defend itself against a possible US invasion.

At the same time, it is under a self-imposed coronavirus blockade, having closed its borders last January to protect against the virus that first emerged in neighbouring China, adding to the pressure on its moribund economy.

And the change of US leadership presents a challenge for Pyongyang. Biden is associated with the Obama administration's "strategic patience" approach and characterised Kim as a "thug" during the presidential debates.

Washington is expected to return to more orthodox diplomatic approaches under Biden, such as insisting on extensive progress at working-level talks before any leaders' summit can be considered.

"It was very well calculated," professor Park told AFP. "Without showing any ICBMs, Kim Jong Un still sent a message on the North's nuclear capabilities and military strengths.

"Kim is saying if the incoming Biden administration does not remove its 'hostile policies' against the North, to the degree that Kim wants, this is the path that the North is willing to take."