Four US F-35B Lightning II stealth jets and two B-1B Lancer strategic bombers flew over Korea on Monday, training with South Korea's F-15K Slam Eagle fighter jets in a show of the alliance's powerful deterrence against North Korea, their militaries announced.

During the mission, the aircraft "flew across the Korean Peninsula and practiced their attack capabilities by releasing live weapons at the Pilsung Range training area" in the eastern province of Gangwon, the US Pacific Command said in a statement.

In particular, they flew in formation near the Demilitarized Zone along the tense inter-Korean border, it added.

The Marine Corps' F-35Bs based in Japan and the Air Force's B-1Bs stationed in Guam are among high-profile US defense assets deployed to Korea relatively often in response to the North's provocations.

But it's highly unusual for the aircraft to approach North Korea.

Hours earlier, South Korea's Air Force also said the allies conducted a "regular deployment" exercise aimed at improving "extended deterrence."

It did not provide details of the exercise including the exact time or venue.

In the training, held from noon till 2:30 p.m. ,the F-35Bs dropped a total of four inert GBU-32 bombs and the B-1Bs laid two live MK-84 bombs. according to a government source here,

It was joined by four South Korean F-15K fighter jets armed with MK-82 bombs, two US Forces Korea's F-16 jets and two KC-135 tanker refueling planes, added the source.

The combined practice came three days after the North fired another intermediate-range ballistic missile over Japan in the wake of a sixth nuclear test early this month.

The allies honed the capability of expeditiously deploying "response forces" by improving their interoperability and combined operation abilities, the Air Force said, as they plan to continue such joint drills.

The US warplanes also had a similar joint training with Japan's F-2 fighter jets in a "sequenced bilateral mission" on Friday.

US dispatched four F-35Bs and two B-1Bs late last month in the wake of the North's ballistic missile launch. (Yonhap)