Four days after North Korea's fifth and possibly most powerful nuclear weapons test, the US Air Force responded with a show of force on Tuesday, flying two powerful, battle-tested B-1 bombers over South Korea, reports CNN.

North Korea claimed Friday's test showed it had a nuclear warhead that could be mounted on ballistic missiles, a possibility that increases fears for US allies in the region and also poses a threat to US bases in South Korea, Japan and Guam.

"North Korea's nuclear test is a dangerous escalation and poses an unacceptable threat," Gen. Vincent K. Brooks, U.S. Forces Korea commander, said in a statement Tuesday. "The United States has an unshakable commitment to defend allies in the region and will take necessary steps to do so, including operations like this one today."

The B-1s were joined by US F-16 and South Korean F-15 fighters in the low-level flyover of Osan Air Base, 64 kilometers south of the South Korean capital of Seoul.

On the diplomatic front, the US special envoy on North Korea, Sung Kim, said Tuesday that the US and South Korea will be considering "additional unilateral measures" in response to Pyongyang's latest nuclear test. Kim also said Japan may be included in additional initiatives.

The B-1s that flew over South Korea Tuesday were moved to the Andersen Air Force base in Guam in August as part of what the U.S. Pacific Command calls it Continuous Bomber Presence.

The US use of Guam-based bombers to make a statement on the Korean Peninsula is not new. After North Korea's fourth nuclear test in January, a Guam-based B-52 made the flight.

In February, after a North Korean rocket sent a satellite into space, the US Air Force flew four of its top-of-the-line F-22 Raptors over South Korea in a show of force. The stealthy F-22s were joined by South Korean F-15s and US Air Force F-16s in that display at Osan AB.

While the B-1s made a strong US statement Tuesday, Brooks, the US commander, pointed out they aren't the only weapon in the US arsenal.

In his statement, the US general also mentioned the deployment to South Korea of the Terminal High Altitude Area Defense system (THAAD), which is designed to shoot down short, medium and intermediate ballistic missiles, just the type of weapons North Korea claims it has.