In Show of Force Against North Korea, US Air Force Bombers Conduct Joint Flights With South Korea, Japan Two B-1 bombers flew within 75 miles of the North Korean border.

 -- Two U.S. Air Force B-1 bombers flew over South Korea near the border with North Korea today to reinforce the U.S. commitment to its regional ally after the North's latest nuclear test.

The supersonic B-1 bombers took off from Andersen Air Force Base in Guam before conducting low-level flights in the vicinity of Osan Air Base near Seoul, just 75 miles from the border with North Korea. The bombers were accompanied by a Korean F-15K fighter aircraft, as well as a U.S. F-16 fighter aircraft.

"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."

Last Thursday, North Korea tested its fifth and possibly largest nuclear weapon, once again violating U.N. Security Council resolutions that prohibit the communist country from using such technology. North Korean state TV declared that the nation had standardized and minimized nuclear warheads and would continue to strengthen its nuclear capabilities.

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.