North Korea has denounced South Korea, the U.S. and Japan for staging combined air drills involving U.S. B-1B bombers, warning that it will “more intensively” exercise its right to self-defense.

The chief of the external policy office of the North’s foreign ministry issued the warning in a statement Friday, stressing that the North will exercise its right to self-defense more intensively to defend its sovereign rights and security interests. 

In the statement, the ministry expressed “serious concern” over what it called provocations by the U.S. and its allies, saying they are destabilizing the Korean Peninsula.

The ministry official said the North’s access to a more overwhelming war deterrent is essential to maintaining the balance of forces on the Korean Peninsula and ensuring the security of the regional situation.

The statement comes two days after the three nations held joint air drills involving two B-1B bombers over the Korean Peninsula.