North Korea's top diplomat says President Donald Trump's tweet that leader Kim Jong Un "won't be around much longer" was a declaration of war against his country by the United States.

Foreign Minister Ri Yong Ho told reporters Monday that what he called Trump's "declaration of war" gives North Korea "every right" under the U.N. Charter to take countermeasures, "including the right to shoot down the United States strategic bombers even they're not yet inside the airspace border of our country."

Ri referred to Trump's tweet Saturday that said: "Just heard Foreign Minister of North Korea speak at U.N. If he echoes thoughts of Little Rocket Man, they won't be around much longer!"

Ri said: "The question of who won't be around much longer will be answered then."