The two American B-1B strategic bombers that flew over North Korea on Wednesday had approached North Korea’s border, US officials say.

The US Pacific Command broke the news on its website on Wednesday, noting that the flight was the closest a B-1 had ever gotten to the border.

South Korean media reported Thursday that both bombers flew over a front-line US firing range located about 30 kilometers (19 miles) from the border.

One of the nuclear-capable supersonic bombers landed at Osan Air Base, near Seoul, the capital of South Korea -- a first in two decades. The four-engine bomber will stay at the base for an unspecified period of time.

North Korea has been at odds with the South since the end of the Korean War of the early 1950s. An armistice ended all military hostilities between the two Koreas back then, but no peace deal ever ensued, meaning that, while the two countries are not at war, they are not at peace, either.

Although the US has a record of sending advanced weaponry to the Korean Peninsula amid heightened tensions between the two neighbors, such flights near the world’s most heavily fortified border are unusual.

On September 13, two other B-1 Lancer strategic bombers took off from an American base in the Western Pacific island of Guam and performed a low-altitude flight over Osan Air Base.

Four days before the bombers were dispatched to the volatile region, Pyongyang had conducted its fifth and biggest ever nuclear test on September 9, which, according to South Korea’s meteorological agency, was almost identical to America’s nuclear bombing of Hiroshima in 1945.

Washington said the demonstration was “just one example of the full range of military capabilities” that the US possessed to counter potential threats from North Korea in the face of the latter’s nuclear and missile tests.

North Korea responded by saying Washington’s provocative moves were pushing the Korean Peninsula to “the point of explosion.”

Pyongyang says it will continue to develop nuclear weapons as a “deterrence” measure against America’s military aggression.