US President Donald Trump doubled down on his warnings to North Korea Thursday, saying his threat to rain "fire and fury" on it maybe "wasn't tough enough."

Speaking alongside Vice President Mike Pence, Trump also said China could do "a lot more" to pressure Pyongyang to end its nuclear weapons program.

Responding to North Korea's dismissal of his dire warnings as "nonsense," Trump told reporters "maybe it wasn't tough enough."

"They've been doing this to our country for a long time, many years," he said. "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."