North Korea on Saturday showed off what it said were long-range ballistic missiles carrying miniaturised nuclear warheads, its latest claim to the sophisticated technology which state television said could destroy enemies in a "sea of fire".

Rows of the intercontinental ballistic missiles known as KN-08, which some think could fly far enough to reach the continental US, were paraded through the capital as part of a massive military parade marking the 70th anniversary of the ruling Workers Party.

A defence analyst in Seoul said the new missile appeared to have been modified to allow it to be fitted with a miniature nuclear warhead -- a claim echoed by North Korea's state TV -- but others experts said it was impossible to tell.

North Korea has long claimed it has technology capable of launching nuclear bombs at its distant enemies, but experts are sceptical whether the impoverished country has acquired the sophisticated technology needed to produce such weapons.

"With the vengeful desire to turn the citadel of our enemies into a sea of fire, our powerful tactical rockets loaded with diversified and miniaturised nuclear warheads are on the move," the commentator said, as rows of missiles were shown on screen.

Leader Kim Jong-Un on Saturday told crowds assembled for the parade that the country's armed forces "are capable of fighting any kind of war provoked by the US and we are ready to protect our people and the blue sky of our motherland".

Lee Il-Woo, a defence analyst at Korea Defence Network, said the new version of the KN-08 -- which has an estimated range of up to 12,000 kilometres (7,500 miles) -- had a more rounded end than the version unveiled in 2012.

"This means North Korea might have successfully developed technology to minimise nuclear warheads and fit them on top of missiles," he told AFP.

But another analyst, Chae Yeon-Seok at the Korea Aerospace Research Institute, cautioned that the missiles might be mock-ups.

"You never know what is inside by just looking at them. It has never been verified that North Korea has developed any nuclear-tipped ICBMs," he said, using a short-hand for intercontinental ballistic missile.

Seoul's Yonhap news agency, quoting military sources, also said it remains unclear whether the warheads on display might be ordinary explosives or nuclear devices.

"Its cone has a different shape now. We need further analysis to determine whether it is filled with ordinary high explosives or a nuclear warhead," the military official said.