Watch: Trump stuns Kim by asking photographers to make them both look 'thin'

US President Donald Trump may have offended his new-found friend Kim Jong Un by appearing to fat-shame the North Korean leader as they met for a working lunch during their historic summit in Singapore.

As the two leaders stood on opposite sides of the table for a photo opportunity, Trump prompted photographers to make them look "handsome and thin".

"Getting a good picture everybody? So we look nice and handsome and thin and perfect," he said.

A video camera then focused on Kim as Trump's comment was translated for him, and the North Korean leader looked taken aback and not amused.

Kim is reportedly tetchy about his weight gain.

Video of the dining room incident has gone viral, and it's not the first time Trump has taken aim at the North Korean leader's weight.

"Why would Kim Jong-un insult me by calling me 'old,' when I would NEVER call him 'short and fat'?" he tweeted last November as tensions between them escalated.

"Oh well, I try so hard to be his friend - and maybe someday that will happen!"

Time will tell.