US President Donald Trump dismissed concerns about recent missile launches from North Korea and said he was confident that the country's leader, Kim Jong-un, would keep promises that he had made.

"North Korea fired off some small weapons, which disturbed some of my people, and others, but not me. I have confidence that Chairman Kim will keep his promise to me," he said on Twitter.

Mr Trump is currently in Japan on a state visit.

The president, who left his second summit with Mr Kim earlier this year in Vietnam without a peace deal, has put enormous value in their personal relationship, despite actions by North Korea that others consider provocative.

Mr Trump is expected to discuss concerns about North Korea's nuclear and missile programmes with Japanese Prime Minister Shinzo Abe during his stay in Tokyo.

In his tweet, the president, who is running for re-election in 2020, knocked his potential Democratic opponent, former Vice President Joe Biden, misspelling his name and taking pleasure in the North Korean leader's sharp rhetoric about a fellow American.

Mr Trump said in the tweet that he smiled when Mr Kim "called Swampman Joe Bidan a low IQ individual, & worse. Perhaps that’s sending me a signal?"

Mr Trump regularly uses derisive nicknames to target his political opponents.

The president’s remarks came after US National Security Adviser John Bolton said yesterday that North Korea's recent missile launches violated a UN Security Council resolution.

Earlier this month Mr Kim oversaw the first flight of a previously untested weapon - a relatively small, fast missile experts believe will be easier to hide, launch and manoeuvre inflight.