South Korea and the US will face even greater security threats should they go ahead with scheduled joint military drills next week, a senior North Korean official said on Tuesday.
The warning came from Kim Yo-jong, sister of North Korean leader Kim Jong-un, before preliminary drills began on Tuesday, the state-run Yonhap news agency reported.
Nuclear-armed North Korea said the exercises would set back progress in improving inter-Korean relations.
The drills are an "unwelcome, self-destructive action" that threaten the North Korean people and raise tensions on the Korean peninsula, Ms Kim said in a statement broadcast by state news agency KCNA.
"The United States and South Korea will face a more serious security threat by ignoring our repeated warnings to push ahead with the dangerous war exercises," she said.
She accused South Korea of "treacherous treatment" over the drills shortly after a hotline between Pyongyang and Seoul was reconnected in an attempt to ease tension.
North Korea's reaction to the exercises could jeopardise efforts by South Korean President Moon Jae-in to reopen a joint liaison office that Pyongyang blew up last year and to hold talks as part of efforts to restore relations.
On Monday, South Korea's Defence Ministry said the timing, scale and formation of the drills were not yet finalised. US Forces Korea declined to comment.
The US stations about 28,500 troops in South Korea as a legacy of the 1950-53 Korean War, which ended in an armistice rather than a peace deal, leaving the peninsula technically in a state of war.
Military exercises have been scaled back in recent years to allow for talks aimed at dismantling Pyongyang's nuclear and missile programmes in return for US sanctions relief, but negotiations collapsed in 2019.
While North Korea and the US say they are open to diplomacy, both also say it is up to the other side to take action.
Ms Kim said US military actions showed Washington's talk of diplomacy was a hypocritical cover for aggression on the peninsula, and that peace would only be possible if the American military force in the South was dismantled.
North Korea will boost its "absolute deterrence", including a "strong pre-emptive strike capability", to counter the increasing military threat, she said.
"The reality has proven that only practical deterrence, not words, can guarantee peace and security of the Korean peninsula, and that it is an imperative for us to build up power to strongly contain external threats," she said.