Two U.S. Air Force B-1B strategic bombers this week made the closest-ever flight to North Korea to warn the communist country against any further provocations, the U.S. Pacific Command (USPACOM) said Thursday.

North Korea conducted its fifth underground nuclear test on Sept. 9, despite international condemnations and sanctions imposed after the previous nuke detonation in January. The latest provocation came on the heels of the launch of three ballistic missiles four days earlier.  

One of the two B-1B Lancers landed on Osan Air Base in Pyeongtaek, 70 kilometers south of Seoul, after flying over the skies of South Korea on Wednesday. The other returned to Andersen Air Base in Guam the same day.

"It was the first time a Lancer landed on the Korean Peninsula in 20 years (since 1996)," the USPACOM's website showed.

The lone B-1B remains at Osan with the Ministry of National Defense saying it does not know when it will fly back to Guam. U.S. Forces Korea (USFK) declined to comment on the departure time.

"What we are showing today (Wednesday) is just one tool we have to choose from a wide array of options. The alliance grows stronger every day and we remain prepared to defend and to preserve the security of the Korean Peninsula and the region," Lt. Gen. Thomas W. Bergeson, 7th Air Force commander, said in a statement released by the USFK. 

Lt. Gen. Lee Wang-keun, South Korea's Air Force Operations commander, said, "Should the enemy provoke us again, the South Korea-U.S. combined forces will respond and eliminate the North's will and capability to fight."

In response to the recent nuclear test by North Korea, the U.S earlier sent two of its four-engine supersonic bombers in a flyover on Sept. 13. At the time the two B-1Bs returned to Guam without landing at the U.S. air base.

The B-1B Lancer, capable of reaching the peninsula from Guam in just two hours, is one of the U.S. military's three major multi-role, long-range bombers along with the B-52 Stratofortress and B-2 Spirit.

There is the possibility that the U.S. will send B-52s and B-2s to Korea as well.

In the past decade, Pyongyang has continued such provocative acts as nuclear tests and long-range rocket launches despite a wide range of U.N.-led sanctions.

On Jan. 10, four days after the North's fourth nuclear test, the U.S. flew a B-52 bomber over South Korea. The B-52 can carry nuclear missiles and "bunker buster" bombs that are capable of destroying the North's underground facilities.

These, including Wednesday's landing, are "just the first steps" in further strengthening the alliance between Seoul and Washington, the USFK said.

North Korea, meanwhile, protested the flyover of the two B-1Bs, saying such actions could result in Seoul being turned into ash.

The General Staff Department of the Korean People's Army (KPA) said that the provocation is testing the North's tolerance, and it has "pushed the situation on the Korean Peninsula to the uncontrollable and irreversible phase of the outbreak of a nuclear war," according to the North's Korean Central News Agency (KCNA).

"The DPRK's access to the treasured nuclear sword is aimed to foil the adventurous nuclear war racket of the U.S. imperialists who have ceaselessly resorted to nuclear threat and blackmail against the DPRK for the last several decades," it said. DPRK is the acronym for North Korea's official name, the Democratic People's Republic of Korea.

"The nuclear warheads fired by the KPA as punishment will completely reduce to ashes Seoul, the center of confrontation with compatriots where Chongwadae is located and reactionary ruling machines are concentrated."

The statement from the KPA also showed their anger against the U.S., saying the country can launch a strike at U.S. territory.

"Should they escalate the danger of military provocations by letting B-1Bs fly over the air of Korea, the KPA will sweep Guam, the base of provocations, from the surface of the earth," it said.

"The U.S. introduction of nuclear war means would put its aggressor forces' bases in the theatres of Pacific operations into a nuclear nightmare."

The KPA said the only way for the U.S. and South Korea to avoid their attack is to "exercise prudence and self-restraint, refraining from infringing upon the latter's dignity and security." (Yonhap)