The warning comes as Seoul and Washington are set to carry out their annual Ulchi Freedom Shield exercises from August 18 to 21.
North Korea has always been infuriated by US-South Korean military drills, decrying them as rehearsals for invasion.
“The armed forces of the DPRK will cope with the war drills of the US and (South Korea) with thoroughgoing and resolute counteraction posture... at the level of the right to self-defense,” North Korean defense chief No Kwang Chol said in a statement carried by the Korean Central News Agency, AFP reported.
The US stations around 28,500 troops in South Korea, and the allies regularly stage joint drills they describe as defensive in nature.
Seoul and Pyongyang have recently appeared to be heading toward a thaw in relations, with the two sides removing propaganda loudspeakers along the border.
Seoul has said North Korean troops have begun dismantling propaganda loudspeakers used to blare unsettling noises along the border, days after Seoul’s new administration dismantled its own.
The two countries had already halted propaganda broadcasts along the demilitarized zone, Seoul’s military said in June, after the election of President Lee Jae Myung, who is seeking to ease tensions with Pyongyang.
Relations between the two Koreas had been at one of their lowest points in years under former president Yoon Suk Yeol, with Seoul taking a hard line toward Pyongyang.
Lee has taken a different approach to dealing with the North since his June election, including requesting civic groups cease sending propaganda leaflets over the border by balloon.