North Korean leader Kim Jong-un has been quoted as saying in a New Year's message that his country's development of banned intercontinental ballistic missiles (ICBM) is in "final stages".

"Research and development of cutting-edge arms equipment is actively progressing and ICBM rocket test launch preparation is in its last stage," Kim said on Sunday.

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 United States.

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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 September 9.

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

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.