"I spoke with President Moon [Jae-in] of South Korea last night," the president wrote.
"Asked him how Rocket Man is doing. Long gas lines forming in North Korea. Too bad!"
The White House said Trump and Moon discussed North Korea’s recent intercontinental ballistic missile (ICBM) launches during a call on Saturday.
"The two leaders noted that North Korea continues to defy the international community, even after the United Nations strongly condemned North Korea’s repeated provocations twice in the past week," the White House said in a statement.
"President Trump and President Moon committed to continuing to take steps to strengthen deterrence and defense capabilities and to maximize economic and diplomatic pressure on North Korea," it added. "The two leaders noted that they will continue their close consultations next week when they meet on the margins of the United Nations General Assembly."
A South Korean official said the leaders agreed on the need for stronger sanctions against North Korea during their call, Reuters reported.