North Korea Could Boast Missile Submarine Fleet Within Five Years

North Korea could be in possession of fully operational missile-launching submarines within five years, the South Korean government has warned.

The estimate comes after North Korea test-launched a ballistic missile fired from a submarine at the weekend which Pyongyang claimed was successful.

The successful test could not be independently verified but if true, it represents a new development in the threat posed by North Korea to Seoul as submarine missiles are harder to detect as they are fired underwater.

A South Korean defence ministry official, speaking on condition of anonymity, told CNN that the South Korean military believes that the photos of the launch released by North Korean media are real.

South Korean defence ministry spokesman Kim Min-seok warned today that the launch was "very serious and a matter of concern," calling for Kim Jong-un to halt the development of such weaponry.

"We judge North Korea's underwater test-firing of a submarine-launched ballistic missile to be very serious and a matter of concern," he said.

"We urge North Korea to immediately stop developing SLBMs (submarine-launched ballistic missiles), which hinder the stability of the Korean peninsula and northeast Asia."

Although North Korea may be able to arm itself with such missiles in the future, South Korea believes that Pyongyang remains in the "early phase" of developing any such weapons.

The US State Department condemned the launch as a "clear violation" of the United Nations sanctions in place against the pariah state. A statement released by the U.S. agency said that North Korea must "refrain from actions that further raise tensions in the region."

Any ballistic missile development by Pyongyang would contravene UN resolutions which prohibit the country from building such technology.

After the missile test, Jong-un said that Pyongyang now owned a "world-level strategic weapon capable of striking and wiping out in any waters the hostile forces infringing upon [North Korea's] sovereignty and dignity", according to state news agency KCNA.

The North Korean military also test-fired three cruise missiles on Saturday a day after the submarine missile launch, as it continues to threaten South Korea's security in what it says is retaliation for territorial breaches by South Korean navy patrols, a charge which Seoul denies.

Both North and South are still technically at war after a ceasefire brought fighting to an end in July 1953 but the two countries remain in a state of armed truce.