U.S. B-1B Lancer bombers flew in international airspace off North Korea's eastern coast in the latest show of force on Sunday as a war of words between the two countries escalated to fever pitch.

The move came after North Korea threatened to detonate a hydrogen bomb in the Pacific Ocean. South Korea's National Security Council met on Sunday amid fears that the U.S. could clash with North Korea.

"This is the farthest north of the DMZ any U.S. fighter or bomber aircraft have flown off North Korea's coast in the 21st century, underscoring the seriousness with which we take [North Korea's] reckless behavior," Pentagon spokeswoman Dana White said.

"This mission is a demonstration of U.S. resolve and a clear message that the president has many military options to defeat any threat. North Korea's weapons program is a grave threat to the Asia-Pacific region and the entire international community."

The U.S. Defense Department did not say how many aircraft were deployed and how far north they traveled, but the Wall Street Journal reported that eight fighter planes were deployed, including two B-1Bs.

They buzzed the North Korean coast just before North Korean Foreign Minister Ri Yong-ho in an address to the UN General Assembly said U.S. President Donald Trump's insults make it "inevitable" to attack the U.S. mainland with rockets.

