The United States said two nuclear-capable B-2 stealth bombers flew “deterrence” missions over South Korea on Thursday, defying apocalyptic threats of retribution from North Korea against ongoing war games, AFP reports..

The deployment of the stealth bombers was intended to send a potent message to Pyongyang about the U.S. commitment to defending South Korea against any aggression, as military tensions on the Korean peninsula soar.

It came shortly after the North severed its last-remaining military hotline with South Korea and put its rocket units on combat status with a threat to target U.S. bases in the Pacific region.

The two B-2s, from Whiteman Air Force Base in Missouri, flew the 13,000-mile (20,800-kilometre) round-trip in a “single continuous mission”, dropping dummy ordnance on a target range in the South, the US military said in a statement.

“This demonstrates the United States’ ability to conduct long-range, precision strikes quickly and at will,” the statement said.

The bombers were participating in South Korean-U.S. military exercises that have incensed North Korea, which has threatened to unleash a second Korean War and launch pre-emptive nuclear strikes on South Korea and the U.S. mainland.

“The United States is steadfast in its alliance commitment to the defense of the Republic of Korea,” the U.S. statement said.

Earlier Thursday, U.S. Defense Secretary Chuck Hagel told his South Korean counterpart that Seoul could rely on all the military protection the United States has to offer — nuclear, conventional and missile defence.

The U.S. and South Korean militaries signed a new pact last week, providing for a joint military response to even low-level provocation by North Korea.