North Korean leader Kim Jong Un has said that the isolated nuclear-capable country is close to test-launching an intercontinental ballistic missile (ICBM).

"Research and development of cutting edge arms equipment is actively progressing and ICBM rocket test launch preparation is in its last stage," Mr Kim said during a televised New Year's Day speech.

North Korea tested ballistic missiles at an unprecedented rate during 2016, although some experts have said it is years away from developing an ICBM fitted with a nuclear warhead capable of reaching the US.

The country has been under UN sanctions since 2006 over its nuclear and ballistic missile tests.

The sanctions were tightened last month after Pyongyang conducted its fifth and largest nuclear test on 9 September.

A successful ICBM test launch would mark a significant step forward for secretive Pyongyang's weapons capability.

In February, North Korea launched a satellite into space, which was widely seen as a test of long-range ballistic missile technology.

ICBMs have a minimum range of about 5,500 km, but some are designed to travel 10,000 km or further.

The US state of California is roughly 9,000 km from North Korea.

However, North Korea has struggled to reliably deploy its intermediate-range Musudan ballistic missile, succeeding just once in eight attempted launches last year.

The Musudan is designed to fly about 3,000 km, posing a threat to South Korea and Japan, and possibly the US territory of Guam.

South Korea's defence ministry declined to comment on whether North Korea would test launch an ICBM soon.

A senior US military official said last month that North Korea appears able to mount a miniaturised nuclear warhead on a missile but is still struggling with missile re-entry technology necessary for longer range strikes.