US Secretary of Defense Jim Mattis said Wednesday that there was still room for diplomacy in dealing with North Korea's provocative ballistic missile launches, after President Donald Trump said negotiations were "not the answer."

"We're never out of diplomatic solutions," Mattis said as he went into a meeting with South Korea Defense Minister Song Young-moo.

The comment came after Pyongyang elevated the crisis over its growing potential nuclear threat with the test launch of an intermediate range ballistic missile over Japanese territory on Tuesday.

Before Mattis spoke, Trump had tweeted: "The U.S. has been talking to North Korea, and paying them extortion money, for 25 years. Talking is not the answer!