North Korean leader Kim Jong-Un has hailed the recent test of a submarine-launched ballistic missile (SLBM) -- which was viewed with wary scepticism outside the reclusive state -- as a miraculous leap forward.

The North's official KCNA news agency reported Tuesday that Kim hosted a gathering of the scientists and technicians who were behind the test that was announced with great fanfare earlier this month.

It said Kim congratulated them for producing an "eye-opening miracle" and a "historical event" that had left the country with a powerful strategic weapon.

A fully developed SLBM capability would take the North Korean nuclear threat to a new level, allowing deployment far beyond the Korean peninsula and the potential to retaliate in the event of a nuclear attack.

But experts have questioned the authenticity of the recent test, saying photos of the launch had been digitally manipulated and suggesting the missile was probably fired from a sunken platform rather than a submarine.

Although the North clearly is set on developing a working SLBM, the expert consensus was that it remains years from acquiring such a capability.

Whether the test was exaggerated or not, South Korea said Tuesday it had requested a UN investigation into whether it constituted a sanctions violation.

Current UN resolutions ban North Korea from developing or using ballistic missile technology.

"We've sent a letter to the UN Sanctions Committee," foreign ministry spokesman Noh Kwang-Il told reporters.

North Korea has been ramping up its nuclear rhetoric of late, boasting last week of its ability to miniaturise a nuclear warhead to fit on a missile.