US nuclear-capable supersonic bombers fly in show of force to North Korea

The seismic waves in North Korea last week believed to have been from a nuclear test. Photo / AP

The United States has flown nuclear-capable supersonic bombers over ally South Korea in a show of force.

The move is meant to cow North Korea after its fifth nuclear test and also to settle rattled nerves in the South.

The B-1 bombers, escorted by US and South Korean jets, were seen by an Associated Press photographer as they streaked over the Osan Air Base, which is 120km from the border with North Korea.

The bombers were likely to return to their base in Guam, without landing in South Korea.

Such flyovers are common during tense times.

South Korea does not have nuclear weapons and relies on the US "nuclear umbrella" as a deterrent to North Korea.

North Korea says US hostility is the reason it needs a nuclear bomb programme.

A US B-1B Lancer (C) is escorted by US F-16 fighter jets as it flies over the Osan Air Base, Pyeongtaek, September 13, 2016. (AFP photo)

The US has flown two heavy bomber jets over South Korea, a move that is expected to stir more tension on the Korean Peninsula following a recent nuclear test by the North.

The B-1 Lancer strategic bombers took off from an American base in Guam on Tuesday and performed a low-altitude flight over Osan Air Base, near Seoul, the South's capital.

American and South Korean fighter jets escorted the B-1s during the low-speed flight, which took place 77 km (48 miles) from the Demilitarized Zone border with the North.

General Vincent Brooks, the commander of the 28,500 US troops in South Korea, said the symbolic flight illustrated the strong military alliance between Washington and Seoul.

US General Vincent K. Brooks (R), commander of the United States Forces Korea, speaks as South Korea's Joint Chiefs of Staff chairman General Lee Sun-jin (L) looks on during a press briefing on the B-1B Lancer flight, September 13, 2016. (AFP photo)

"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 American commander said in a statement.

The fly-over came days after Pyongyang conducted its fifth and biggest “nuclear warhead explosion” test on Friday, which, according to South Korea’s meteorological agency, was almost identical to America’s nuclear bombing of Hiroshima in 1945.

The test intensified an ongoing military standoff between the US and North Korea, which was ignited by Washington’s deployment of sophisticated weaponry to the South.

North Korea has pledged to develop a robust nuclear arsenal to protect itself from the US military. Washington, in turn, has stepped up its military presence in the region under the pretext of defending Seoul.

US President Barack Obama rushed to condemn the North’s fifth test, saying Friday that it posed "a grave threat to regional security and to international peace and stability."

He pledged to push for new sanctions against the Pyongyang regime, which has already been hit by five sets of UN sanctions since it first tested a nuclear device in 2006.

It remains to be seen if Obama will succeed in his quest for more sanctions since China, a major supporter of the North, believes such actions can only lead to a dead end.