The planes flew Wednesday over the Yellow Sea -- located between China and the Korean peninsula -- in the first such exercises this year, the agency said, quoting South Korea's military.

The display of military power came a day after US Defence Secretary Lloyd Austin and his counterpart from the South warned of an increase in such drills and more security cooperation between the two allies as they grapple with what they call rising missile and nuclear threats from Pyongyang.

The latest drills involved a B-1B strategic bomber and F-22 and F-35B stealth fighter planes from the US Air Force and F-35A fighter planes from the South Korean military, Yonhap said.

"The combined air drills this time show the US' will and capabilities to provide strong and credible extended deterrence against North Korea's nuclear and missile threats," Yonhap quoted the defence ministry as saying.

The agency said extended deterrence refers to the US commitment to use a full range of military assets, including nuclear weapons, to defend South Korea.

Seoul is eager to convince its increasingly nervous public of America's robust defence commitment, after a year in which North Korea declared itself an "irreversible" nuclear power and conducted a banned weapons test almost every month.

Austin and South Korean Defence Minister Lee Jong-sup agreed to "expand and bolster the level and scale" of joint military exercises, in light of "continued provocations" from Pyongyang, including a recent drone incursion, they said in a statement Wednesday.

Military tensions on the Korean peninsula intensified sharply in 2022 as the North conducted a record-breaking number of weapons tests, including firing its most advanced intercontinental ballistic missile.

Any joint US-South Korean military exercises infuriate Pyongyang, which views them as a rehearsal for an invasion and has often responded with threats and drills of its own.