North Korea's official news agency is reporting that plans by South Korea and the United States to conduct joint military exercises are pushing the peninsula to "the brink of war".
The statement comes just days after a deadly artillery attack by the North on the tiny South Korean island of Yeonpyeong, in which four people were killed. The Communist state later claimed it was retaliating after South Korea had staged military exercises.
A US carrier strike group, based in Japan, is heading for waters west of the Korean peninsula where the US and South Korea plan four days of naval exercises in the Yellow Sea from Sunday.
There have also been political repercussions, with South Korea naming a presidential security aide as Defence Minister, after his predecessor Kim Tae-young quit.
He stepped down after taking responsibility for the widely-criticised response to an attack by North Korea earlier this week.
The new minister is Lee Hee-Won, who's the security adviser to President Lee Myung Bak.
He is a career military man who is said to be on good relations with the US, South Korea's biggest ally.
Mr Lee, 61, is a former four-star general who became deputy chief of the US-South Korea Joint Forces Command in 2005.
He retired from the military in 2006 and was made a presidential security advisor in May following the sinking of the Cheonan, a South Korean warship.
This week's artillery shelling - which killed two civilians and two marines - was one of the worst incidents between the two Koreas since the end of the Korean war in 1953, which concluded without a peace treaty.
The president accepted Mr Kim's resignation "to improve the atmosphere in the military and to handle the series of incidents," a presidential official said.
In response to Tuesday's incident, South Korea has increased troop numbers on Yeonpyeong, and has said it is changing its rules of engagement to allow it to respond more forcefully to similar incidents. The old rules have been criticised as too passive.