North Korean leader Kim Jong-un says the nation will continue to develop “formidable striking capabilities” that cannot be bartered or sold for anything, the country’s state media reports.

Mr Kim had met officials, scientists, technicians and workers who contributed to a missile launch on Thursday, which North Korea said was a test firing of its largest intercontinental ballistic missile, state news agency KCNA said.

“Only when one is equipped with the formidable striking capabilities, overwhelming military power that cannot be stopped by anyone, can one prevent a war, guarantee the security of the country and contain and put under control all threats and blackmails by the imperialists,” Mr Kim said, according to the report.

While personally overseeing the test on Thursday, Mr Kim said the new ICBM was to help deter any military moves by the US, which remains technically at war with the North after the 1950-1953 Korean War ended in an armistice rather than a peace agreement.

Washington has sought to pressure Pyongyang into surrendering or reducing its arsenal of nuclear weapons and ICBMs, which may be able to strike targets in the US.

But Mr Kim said his self-defence force “cannot be bartered nor be bought with anything” and will be held firm despite harsh trials and difficulties.

North Korea would continue to build a “more perfect and stronger strategic force”, Mr Kim said, referring to the country’s nuclear program.

The US said on Friday it would push for United Nations sanctions on North Korea to be strengthened because of the “increasingly dangerous provocations”. But China and Russia have signalled opposition and instead argued for measures to be eased.

North Korea said Thursday’s missile was the Hwasong-17, with Japan and South Korea confirming flight data showed the launch flew higher and longer than any previous North Korean test.

But analysts said state media coverage appeared to be trying to pass off footage from a previous launch. South Korea’s Yonhap news agency reported on Sunday that intelligence officials in Seoul and Washington believe the North actually tested an older and slightly smaller Hwasong-15 missile.

-AAP