SEOUL, April 17 (UPI) — North Korea warned Thursday it would respond with “overwhelming deterrence” against the United States following Washington’s deployment of B-1B strategic bombers to the Korean Peninsula for a joint air exercise with South Korea this week.

The allies’ drills represent an “open threat to the security of our state and a grave provocation that raises the military tension in the region to an extreme dangerous level,” a spokesperson for North Korea’s Defense Ministry said in a statement carried by state-run Korean Central News Agency.

“The DPRK will exercise the overwhelming deterrence and continue to make the U.S. recognize that its unannounced deployment of strategic means is a reckless and unnecessary abuse of strength,” the spokesperson said, using the official acronym for North Korea. “The higher the level of provocation against the DPRK is, the greater the level of danger returning to the U.S. will be.”

The United States sent a pair of B-1B strategic bombers to participate in joint drills on Tuesday, which was a holiday in North Korea marking the birthday of founder Kim Il Sung. The exercise was intended to “respond to the continuous threat of North Korea’s increasingly sophisticated nuclear and missile programs,” Seoul’s Defense Ministry said.

Pyongyang has frequently objected to the deployment of U.S. strategic assets to the Korean Peninsula and condemns the allies’ joint military exercises as rehearsals for an invasion.

The ministry spokesperson said Thursday that the latest exercise was a “process of increasing the skillfulness in tactics and procedures for attacking the DPRK, and completing preparations for going into real action at any time.”

North Korea “will never tolerate the slightest sign of threat of the hostile forces against the security sovereignty of the state,” the spokesperson added.

The drills marked the second deployment of U.S. B-1B bombers to the peninsula since President Donald Trump returned to office. Days after a February joint air exercise, Pyongyang test-fired strategic cruise missiles in what it called a demonstration of its nuclear deterrence capabilities.

North Korea’s statement came as the United States and South Korea kicked off a two-week joint air exercise, called Freedom Flag, on Thursday.

The exercise, which runs until May 2, involves some 1,100 troops and 90 aircraft from both militaries, South Korea’s air force said in a press release. Assets mobilized for the drills include South Korean F-35A, F-15K and KF-16 fighter jets and American F-16 and F-35 B fighters.

The allies “plan to strengthen interoperability and cultivate capabilities for wartime joint mission execution,” the release said. “In addition, they will intensively review and master the latest tactical and operational procedures that reflect the changes in the operational environment of modern warfare.”