SEOUL, Sept. 18 (Xinhua) -- The U.S. forces on Monday dispatched four stealth fighter jets and two strategic bombers to the Korean Peninsula to conduct a joint bombing drill with South Korea's air force, local media reported.

An unidentified South Korean government source was quoted by Yonhap news agency as saying four F-35B stealth combat planes and two B-1B strategic bombers simultaneously made sorties to the peninsula earlier in the day.

The strategic U.S. weapons carried out a mock bombing exercise before returning to unidentified bases, the source was quoted as saying.

The U.S. bombers and combat planes staged a joint exercise with four F-15K fighter jets of South Korea's air force.

The mobilization of U.S. strategic military assets to the peninsula marked the first time since the Democratic People's Republic of Korea (DPRK) detonated its sixth nuclear device on Sept. 3.

Pyongyang flew an intermediate-range ballistic missile (IRBM) over Japan last Friday.

It followed the unanimous approval by UN Security Council of a new resolution toughening sanctions on Pyongyang over its sixth nuclear detonation.