"The United States and the Republic of Korea are taking actions every day to strengthen our alliance and respond to North Korea's continued aggressive behavior," Gen. Vincent Brooks said in a press release. "Today's demonstration provides just one example of the full range of military capabilities in the deep resources of this strong alliance to provide and strengthen extended deterrence. The alliance military forces remain ready to meet mutual defense obligations against threats to the security of the Korean Peninsula and the region."
President Barack Obama issued a condemnation, calling North Korea's actions "provocative and destabilizing," and assured U.S. allies in the region of Washington's "unshakable commitment" to their defense.
Just days before that test, North Korea fired three ballistic missiles into the Sea of Japan. That launch was timed to coincide with the G-20 economic summit held in China and attended by Obama.
Before B-1 bombers flew over Osan Air Base today, they conducted fighter interceptor training alongside Japanese F-2 fighter aircraft, according to U.S. Pacific Command. The sequenced flights with two U.S. allies were meant to demonstrate how the U.S. can work with both nations militarily.
"These flights demonstrate the solidarity between South Korea, the United States and Japan to defend against North Korea's provocative and destabilizing actions," said Adm. Harry B. Harris Jr., the commander of U.S. Pacific Command, in a press release.
"U.S. joint military forces in the Indo-Asia-Pacific are always ready to defend the American homeland," he added. "We stand resolutely with South Korea and Japan to honor our unshakable alliance commitments and to safeguard security and stability."
U.S. flyovers are not uncommon after North Korean tests. After North Korea's fourth nuclear test, in January, the U.S. responded by conducting a similar flyover with a B-52 bomber.
ABC News' Luis Martinez contributed to this report.