North Korea 'test-fires submarine-launched ballistic missile'

North Korea has test-fired what appears to be a submarine-launched ballistic missile off its eastern coast, South Korea has said.

An official at Seoul's defence ministry on Saturday could not immediately confirm how far the projectile travelled and where it landed.

North Korean efforts to develop submarine-launched missile systems are a serious concern for rivals and neighbours because missiles from submerged vessels are harder to detect in advance.

The launch came a day after US and South Korean military officials said they are ready to deploy an advanced US missile defence system in South Korea to cope with North Korean threats.

The missile was fired from near the North Korean coastal town of Sinpo, where analysts have previously detected efforts by the North to develop submarine-launched ballistic missile systems, the defence ministry official said.

South Korea's Joint Chiefs of Staff said it presumed the missile successfully ejected from the submarine's launch tube, but failed in its early stage of flight.

South Korea's Yonhap news agency said the missile probably flew only a few miles before exploding in midair.

North Korea acquiring the ability to launch missiles from submarines would be an alarming development for its neighbours because missiles from submerged vessels are harder to detect in advance.

While security experts say it is unlikely that North Korea possesses an operational submarine capable of firing missiles, they acknowledge the North is making progress on such technology.

North Korea already has a considerable arsenal of land-based ballistic missiles and is believed to be advancing its efforts to miniaturise nuclear warheads mounted on missiles through nuclear and rocket tests.

North Korea last test-fired a submarine-launched ballistic missile in April, calling it as a success that strengthened its ability to attack enemies with "dagger of destruction".

South Korean defence officials then said that the missile flew about 19 miles before exploding in midair.

The North also test-fired a submarine-launched ballistic missile on Christmas Day, but that test was seen as failure, the South's Joint Chiefs of Staff said. The North first claimed a successful submarine-launched missile test in May last year.

Seoul and Washington launched formal talks on deploying the Terminal High-Altitude Area Defence, or THAAD, after North Korea conducted a nuclear test and a long-range rocket launch earlier this year.

China, Russia and North Korea all say the THAAD deployment could help US radars spot missiles in their countries.

The deployment decision for THAAD came after North Korea reacted angrily to new US sanctions on leader Kim Jong Un and other senior officials for human rights abuses.

Pyongyang's foreign ministry said on Thursday such measures were tantamount to declaring war.

North Korea has already been sanctioned heavily because of its nuclear weapons programme.

However, the action by the US on Wednesday marked the first time Kim has been personally targeted, and also the first time that any North Korean official has been blacklisted by the US Treasury in connection with reports of rights abuses.

The United States stations about 28,500 troops in South Korea as deterrence against potential aggression from North Korea.