North Korea submarine launches ballistic missile

North Korea has fired a ballistic missile from a submarine off its east coast, according to US and South Korean officials.

The KN-11 missile was launched from waters near Sinpo and flew about 500km before falling into the Sea of Japan, a US official said.

Japan's Prime Minister Shinzo Abe said it fell inside Japan's Air Defence Identification Zone, calling it a "reckless act".

It comes as South Korea and the US begin annual military drills, which routinely anger Pyongyang.

Ulchi Freedom involves about 80,000 US and South Korean troops in a largely computer-simulated defence of South Korea from a fictional North Korean invasion.

The launch took place at 5:30 a.m. local time, according to a statement from the South Korean Foreign Ministry.

"If the North Korean regime continues to pursue its nuclear and missile capabilities and ignore severe economic difficulties of its people, it will bring about more severe sanctions and diplomatic isolation. It should also realize that it will hasten its self-destruction," South Korea's Foreign Ministry said.

"Our government is prepared with full readiness posture to protect our people and the safety of our country and will thoroughly respond to any North Korea's provocation."

Last month, the US and South Korea agreed to deploy a missile defence system to counter threats from the North.

North Korea has conducted four nuclear tests to date - its most recent claimed to have used a hydrogen bomb - but despite its claims, it is not yet believed to have the ability to mount a nuclear device onto a warhead.

Pyongyang has also been angered recently by several high profile defections, including its deputy ambassador to the UK, Thae Yong-ho.

Thae, thought to be the highest-ranking North Korean official ever to defect, was branded "human scum" by Pyongyang.