The United States said two nuclear-capable B-2 stealth bombers flew "deterrence" missions over South Korea on Thursday.

The United States said two nuclear-capable B-2 stealth bombers flew "deterrence" missions over South Korea on Thursday.

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-US 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 US mainland.

"The United States is steadfast in its alliance commitment to the defense of the Republic of Korea," the US statement said.

The deployment of the stealth bombers was intended to send a potent message to North Korea about the US commitment to Seoul against Pyongyang, as military tensions on the Korean peninsula soar.