After North Korea's leader Kim Jong Un called Donald Trump "old," the president of the United States responded by calling Kim "short and fat."

Kham / AP President Trump participates in a press conference at the Presidential Palace in Hanoi, Vietnam, Sunday.

President Donald Trump traded petty insults with North Korea's supreme leader Kim Jong Un Sunday, but told reporters shortly after that perhaps he and the dictator will one day be friends. "Why would Kim Jong-un insult me by calling me 'old,' when I would NEVER call him 'short and fat?'" Trump tweeted Sunday after arriving in Hanoi, Vietnam. "Oh well, I try so hard to be his friend - and maybe someday that will happen!"

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… https://t.co/PmsWNkH4r4

Trump followed up his bizarre tweet by telling reporters that it would be a "good thing" for him and Kim to become friends. "Might be a strange thing to happen but it's certainly a possibility," Trump said during a press conference with Vietnam's president, adding that it would be "very, very nice if it did."

The president appeared to be responding to a statement from North Korea's foreign ministry Saturday, which warned that "Reckless remarks by an old lunatic like Trump will never scare us or stop our advance." The ministry was reacting to Trump's speech in South Korea last week, in which the president warned North Korea not to test the resolve of the US and its allies.

Wong Maye-e / AP