The US long-range heavy bomber flew over South Korea on Sunday. The flight comes days after North Korea conducted its first alleged hydrogen bomb test.
The US military said that a B-52 Stratofortress, briefly flew over Osan Air Base, some 72 kilometers (45 miles) south of the border between North and South Korea. The plane is capable of carrying nuclear weapons,
It was escorted by a South Korean F-15 and US F-16 fighters.
The B-52 circled once over the base before heading back to Andersen Air Base in Guam, where it is stationed.
"This was a demonstration of the ironclad US commitment to our allies in South Korea, in Japan, and to the defense of the American homeland," said Admiral Harry B. Harris Jr., commander US Pacific Command, in a statement. "North Korea's nuclear test is a blatant violation of its international obligations."
There was no immediate reaction from North Korea's state media to the flyover.
The aircraft are known to have taken part in joint annual US-South Korea military exercises that have enraged Pyongyang, but their flights over South Korea are rarely publicized.
The last time such a flight was made public was in 2013, after North Korea carried out its third nuclear test.
At that time, the US dispatched both a B-52 and the more sophisticated B-2 stealth bomber to South Korea in a show of military muscle against the North.
Pyongyang on Wednesday conducted its fourth nuclear test, angering the international community and raising tensions across the inter-Korean border.
The military exercises which take place annually always garner angry reactions from North Korea, which brands them "nuclear war drills" against it.
The two Koreas remain in a technical state of war after their 1950-53 conflict ended in a truce, not a peace treaty. The United States has about 28,500 troops based in South Korea.
av/ng (AP, AFP, DPA)