Leader Kim Jong Un watched the huge ICBM roll through Pyongyang at the climax of an unprecedented night-time parade on Saturday, weeks before the US election.

"It is disappointing to see the DPRK (North Korea) continuing to prioritize its prohibited nuclear and ballistic missile program," a US official said.

"The United States remains guided by the vision President Trump and Chairman Kim set forth in Singapore (in 2018) and calls on the DPRK to engage in sustained and substantive negotiations to achieve complete denuclearization."

Analysts said that it was the largest road-mobile, liquid-fuelled missile anywhere in the world, and was likely to be designed to carry multiple warheads in independent re-entry vehicles (MIRVs).

The ICBM was proof that the North had continued to develop its arsenal throughout the diplomatic process, analysts said, and could give Pyongyang greater heft to demand a return to the negotiating table.

The missile -- which may have been a mock-up -- was carried on an enormous and previously unseen 11-axle transporter-erector-launcher, far larger than the eight-axle Chinese-made vehicles the North has employed so far.

Nuclear negotiations between Trump and Kim have been deadlocked since the collapse of their Hanoi summit early last year over sanctions relief and what the North would be willing to give up in return.