Seoul and Washington are in a security alliance Image Credit: Reuters

North Korea could consider a change of approach if the US maintains its sanctions on the nuclear-armed country, leader Kim Jong Un warned in his New Year speech Tuesday after 12 months of diplomatic rapprochement.

"If the US does not keep its promise made in front of the whole world... and insists on sanctions and pressures on our republic," Kim said, "we may be left with no choice but to consider a new way to safeguard our sovereignty and interests".

Kim was referring to his summit with US President Donald Trump in Singapore in June, when he said he had "fruitful talks" and "exchanged constructive ideas".

At the time the two leaders signed a vaguely-worded pledge on denuclearisation of the Korean peninsula, but progress has since stalled with Pyongyang and Washington arguing over what that means.

The North is subject to multiple sets of United Nations Security Council sanctions over it banned nuclear and ballistic missile weapons programmes, which have seen it carry out six atomic tests and launch rockets capable of reaching the entire US mainland.

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"I am ready to sit with the US President again at any time in the future and will make efforts by all means to produce a result that will be welcomed by the international community," Kim said in his address, broadcast by the North's state television.

But he said the US and South Korea should no longer carry out joint military exercises - which have been largely halted since the Singapore meeting - calling such drills "a source of tension".

"War-related equipment - including strategic assets of outside powers - should no longer be allowed to be brought in," he added.

Seoul and Washington are in a security alliance and the US stations 28,500 troops in the South to protect it against its neighbour, which invaded in 1950.