North Korean leader Kim Jong Un has guided a special operations drill targeting the South, the North's media reports.
It comes as rival South Korea remained on alert for any attempt by the North to take advantage of political turmoil in the South.
The North's KCNA state news agency report did not say when North Korean forces conducted the combat exercise, nor did it mention the South Korean parliament's vote on Friday to impeach its president, Park Geun-hye.
Pictures in a Sunday report on the exercise in the North's Rodong Sinmun newspaper showed what appeared to be a mock-up of South Korea's presidential Blue House as a target.
Park will remain in the Blue House, though her powers have been suspended and assumed by the South's prime minister while the Constitutional Court weighs parliament's impeachment vote.
South Korean Prime Minister Hwang Kyo-ahn has urged a high state of military alert in case of any provocation by North Korea, including possible cyber attacks.
"We are ready to retaliate if North Korea makes any provocations and we condemn its malicious threat," a South Korean military official told Reuters.
Tension on the divided Korean peninsula has been high this year after two North Korean nuclear tests and an unprecedented flurry of ballistic missile tests.
The North's tests have brought tighter UN Security Council sanctions but no indication North Korea and its young leader Kim are willing to compromise on its nuclear and missile programmes.
The Rodong Sinmun pictures included one of Kim observing the exercise through binoculars.
"Watching the brave service personnel independently and pro-actively perform their combat duty destroying specified targets of the enemy, he said with a broad smile on his face: 'Well done, the enemy troops will have no space to hide themselves, far from taking any counteraction'," KCNA cited Kim saying.
