Four F-35B stealth jets and two B-1B strategic bombers from the United States trained with South Korea’s F-15K fighter jets over the Korean Peninsula on Thursday in response to North Korea’s continued ballistic missile launches and nuclear weapons development, the South’s Air Force announced.

The B-1Bs were flown in from Andersen Air Force Base in Guam while the F-35s came from a U.S. base in Iwakuni, Japan, an official from Seoul’s Defense Ministry said.

They staged air-to-ground precision-strike drills against the North’s core facilities over the Pilseung Range in the eastern mountainous province of Gangwon. They used MK-84, MK-82 and GBU-32 bombs.

The F-35 Lightning II is a 5th Generation fighter, combining advanced stealth with fighter speed and agility, fully fused sensor information, network-enabled operations and advanced sustainment. Three variants of the F-35 will replace the A-10 and F-16 for the U.S. Air Force, the F/A-18 for the U.S. Navy, the F/A-18 and AV-8B Harrier for the U.S. Marine Corps, and a variety of fighters for at least ten other countries.