The U.S. military flew two strategic bombers over the Korean peninsula in a show of force, as President Donald Trump met top defense officials to discuss how to respond to any threat from North Korea.

Tensions have soared between the United States and North Korea following a series of weapons tests by Pyongyang and a string of increasingly bellicose exchanges between Trump and North Korean leader Kim Jong Un.

The two U.S. Air Force B-1B bombers were joined by two F-15K fighters from the South Korean military after leaving their base in Guam, South Korea’s Joint Chiefs of Staff said.

North Korea has launched two missiles over Japan and conducted its sixth nuclear test in recent weeks as it fast advances toward its goal of developing a nuclear-tipped missile capable of hitting the U.S. mainland.

The two U.S. Air Force B-1B bombers were joined by two F-15K fighters from the South Korean military after leaving their base in Guam, South Korea’s Joint Chiefs of Staff said in a statement on Wednesday.

After entering South Korean airspace, the two bombers carried out air-to-ground missile drills in waters off the east coast of South Korea, then flew over the South to waters between it and China to repeat the drill, the release said.

The U.S. military said in a separate statement it conducted drills with Japanese fighters after the exercise with South Korea, making it the first time U.S. bombers have conducted training with fighters from both Japan and South Korea at night.

The U.S. bombers had taken off from the Andersen Air Force Base in Guam. In August, Pyongyang threatened to fire intermediate-range missiles toward the vicinity of Guam, a U.S. Pacific territory that is frequently subjected to sabre-rattling from the North.