Trump to Jong-Un: My nuke button is bigger than yours

US President Donald Trump warned Kim Jong-Un that he has a "much bigger" nuclear button than the North Korean leader following a similar threat from Pyongyang.

It comes as North Korea called on its Southern neighbour to open a border hotline at 6:30am for inter-Korean dialogue. 

"North Korea's KCTV said the North will open a dialogue channel with the South at 3:30 p.m. (0630 GMT) today", a South Korean Unification Ministry spokesman told AFP.

Hours earlier, Washington dismissed the prospect of high-level talks between North and South Korea, as Trump launched the highly personal attack on Twitter on Tuesday.

US ambassador to the UN Nikki Haley described proposed dialogue between North and South Korea as a "band-aid" and said Washington would never accept a nuclear-armed Pyongyang.

Trump tweeted: "North Korean Leader Kim Jong Un just stated that the 'Nuclear Button is on his desk at all times.'

"Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!"

Trump was referring to Kim's annual New Year address, when the leader warned the US he has a "nuclear button" on his table.

Yet he expressed an interest in dialogue and taking part in the Pyeongchang Games next month.

South Korea has responded positively to Kim's overture, suggesting 9 January as a date for rare talks aimed at easing tensions on the Korean Peninsula. 

But the US questioned whether talks could be taken seriously. 

Trump's tweet was also the latest in a series of personal insults the two leaders have traded since the US president took office a year ago.

Trump has mocked Kim as "fat" and a "little rocket man". Kim, for his part has described Trump as a "mentally deranged US dotard".