North Korean leader Kim Jong-Un watched the missile test.

AFP/Seoul

North Korea said on Saturday it had successfully test-fired a submarine-launched ballistic missile (SLBM) - a technology that could eventually offer the nuclear-armed state a survivable second-strike capability.

North Korean leader Kim Jong-Un, who personally oversaw the test, hailed the newly developed missile as a "world-level strategic weapon", according to a report by the official KCNA news agency.

There was no immediate independent confirmation of the test, which would violate UN sanctions banning Pyongyang from using ballistic missile technology.

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.

Satellite images earlier this year had shown the conning tower of a new North Korean submarine, which US analysts said appeared to house one or two vertical launch tubes for either ballistic or cruise missiles.

The same analysts from the US-Korea Institute at Johns Hopkins University said at the time that developing an operational SLBM capability would be extremely costly and likely take North Korea "years" to achieve.

Sooner than expected  

"If this is what North Korea claims it is, then it has come much sooner than anyone expected," said Dan Pinkston, Korea expert at the International Crisis Group in Seoul.

"An SLBM capability would certainly increase the credibility of the North's retaliatory threat, but I'd like to see what foreign intel says about this test," Pinkston said.

According to the KCNA report, the test was carried out by a sub that dived to launch depth on the sounding of a combat alarm.

"After a while, the ballistic missile soared into the sky from underwater," the agency said.

It gave no detail of the size or range, nor did it specify when or where the launch was carried out.

Pictures released by KCNA showed a missile firing out of the water, with Kim Jong-Un watching from a boat in the foreground.

Red lettering on the side of the missile read "bukgeungsong," meaning "north star," or possibly "polaris".

North Korea has been known to doctor military photos, and the validity of the KCNA pictures could not immediately be verified.