President Trump says North Korea "better get their act together" or they will be in trouble "like few nations have ever been".
Mr Trump also referenced his recent "fire and fury" warning to Kim Jong Un's regime.
"It's about time that somebody stuck up for the people of this country and for the people of other countries, so if anything, maybe that statement wasn't tough enough," he said.
The President was speaking after a meeting with security advisers following North Korea's threat to fire missiles towards the US territory of Guam.