Nuclear-armed aircraft are flown over the Korean Peninsula by the Pentagon.

The US deployed B-52 strategic bombers as part of military exercises with South Korea on Wednesday, prompting a warning from North Korea that Washington’s increased military activity in the region could cause tensions to reach boiling point. The South Korean Defense Ministry said the maneuvers marked the first time in a month that the nuclear-capable aircraft had flown over the peninsula. US Seventh Air Force Commander Lt. Gen. Scott L. Pleus claimed that ties with South Korea are “stronger than ever,” and that their respective air forces are capable of completing any mission they will be tasked with. North Korean state news agency KCNA responded to the drills in an article on Thursday, warning that the actions by Washington and Seoul could lead the situation on the peninsula to an irreversible catastrophe. The US previously deployed B-52 bombers to the region in early March and December of last year.

Washington and Seoul have insisted their joint drills are defensive in nature and are intended as a response to the recent uptick in Pyongyang’s missile tests. The North has claimed that the two nations are rehearsing for a war of aggression.