SEOUL, South Korea — American warplanes flew close to North Korea’s coast on Saturday, the same day that the North’s foreign minister told the United Nations General Assembly that President Trump’s threats against the country were “making our rocket’s visit to the entire U.S. mainland inevitable all the more.”

On Twitter, Mr. Trump responded to Foreign Minister Ri Yong-ho’s speech with yet another threat. Saying he had heard Mr. Ri’s speech, and using his recently coined nickname for the North’s leader Kim Jong-un, Mr. Trump wrote: “If he echoes thoughts of Little Rocket Man, they won’t be around much longer!”

Earlier Saturday, the Pentagon said the Air Force had sent B-1B bombers and F-15C fighters over waters north of the Demilitarized Zone separating the two Koreas, in response to what it called the North Korean government’s “reckless behavior.” It was the farthest north “any U.S. fighter or bomber aircraft have flown off North Korea’s coast in the 21st century,” Dana W. White, the Defense Department’s chief spokeswoman, said in a statement.

“This mission is a demonstration of U.S. resolve and a clear message that the president has many military options to defeat any threat,” Ms. White added.