Even on foreign soil, U.S. President Donald Trump — a notorious creature of habit — doesn't stray too far from his Saturday morning ritual: firing off tweets that routinely shake up the geopolitical order.

Trump on Saturday continued this practice by extending an invitation via Twitter to North Korean dictator Kim Jong Un to meet him when he visits the Demilitarized Zone, which separates the two Koreas, this weekend.

Asked at a news conference about the possible meeting after the conclusion of the Group of 20 summit in Osaka — his second visit to Japan in two months — Trump said he would have "no problem" stepping into North Korea if he meets Kim.