US President Donald Trump has begun to put Twitter's expanded 280-character limit to good use, mocking North Korean leader Kim Jong-un in one of his tweets after the social media giant's move to double the word limit.

Referring to Kim's ridicule of Trump by calling him a "dotard" – meaning a senile or old person – the American leader shot back with a tongue-in-cheek tweet early on Sunday, 12 November, saying that he would never call the North Korean supreme commander "fat and short".

Two months ago, Kim had originally called Trump a "dotard" as the two leaders have engaged in a war of words. But the Korean Central News Agency (KNCA), Pyongyang's state-run media outlet, repeated the offensive remark in a statement on Saturday, 11 November.

Responding to that, Trump wrote, "Why would Kim Jong-un insult me by calling me 'old', when I would NEVER call him 'short and fat'? Oh well, I try so hard to be his friend – and maybe someday that will happen."

The US president is currently in Vietnam as part of his 12-day-long Asia visit – which has been mostly dominated by threats emerging from the reclusive North Korean regime. Pyongyang has been keeping a close watch on Trump's tour and has frequently released statements criticising Washington and Trump.

"His current trip to our surrounding region is a warmonger's visit for confrontation to rid the DPRK [the Democratic People's Republic of Korea – North Korea's official name] of its self-defensive nuclear deterrence. It is also nothing but a business trip by a warmonger to enrich the monopolies of the US defence industry by milking the moneybags from its subordinate 'allies'," the KNCA said.

It went on, "The reckless remarks by a dotard like Trump can never frighten us or put a stop to our advance. This rather gives us an assured conviction that our choice to embark on the road of simultaneously promoting the economic construction and the up-building of the nuclear force was all the more a righteous one, and it pushes us to speed up the efforts to accomplish the great cause of completing the state nuclear force."