WASHINGTON (Web Desk) - The United States flew a B-52 bomber over South Korea on Sunday to show its presence in the region, days after North Korea said it successfully tested a hydrogen bomb.
The B-52 swooped over an air base close to the North-South border, according to the BBC.
On Wednesday, Pyongyang said it detonated an underground device, but experts remain sceptical about the claim.
Screens in Seoul show the earthquake near North Korea's nuclear facility.
After North Korea's third nuclear test in 2013, the US took the unusual step of sending its most powerful warplanes - B-2 stealth bombers, F-22 stealth fighters and B-52 bombers - to drills with South Korea in a show of force. B-2 and B-52 bombers are capable of delivering nuclear weapons.
It may take weeks or longer to confirm or refute the North's claim that it successfully tested a hydrogen bomb, which would mark a major and unanticipated advance for its still-limited nuclear arsenal. Outside experts are skeptical the blast was a hydrogen bomb, but even a test of an atomic bomb would push North Korea closer to building a nuclear warhead small enough to place on a long-range missile.
North Korean leader Kim Jong-un said the test was an act of self-defence to prevent nuclear war with the US.
"It is the legitimate right of a sovereign state and a fair action that nobody can criticise," he was quoted by North Korean state media as saying.
Following the test, South Korea resumed broadcasting propaganda from speakers mounted on the border and the North countered with similar broadcasts.
The two sides are technically still at war, with the civil conflict that ended in 1953 concluding in a truce rather than a peace treaty.
The US is an ally of the South and said the B-52's flight was a response "to recent provocative action by North Korea".
Lt Gen Terrence O'Shaughnessy said the US was "steadfast" in its commitment to defending South Korea, and that includes "extended deterrence provided by our conventional forces and our nuclear umbrella".
There has been no response yet from North Korea to the B-52's flight.
