The North has for months been criticising the South's President Lee Myung-Bak in extreme terms and threatening "sacred war" over perceived insults.
There have been no incidents but the language has become increasingly vitriolic. Some analysts said they believe a military provocation is likely.
"The special actions of our revolutionary armed forces will start soon to meet the reckless challenge of the group of traitors," said a statement on the official news agency.
The North said its targets are "the Lee Myung-Bak group of traitors, the arch criminals, and the group of rat-like elements including conservative media destroying the mainstay of the fair public opinion".
It said the actions "will reduce all... to ashes in three or four minutes... by unprecedented peculiar means and methods of our own style".
North Korea is trying very hard to make good on their long-standing threat to turn Seoul into a sea of fire.
We need an iron ring around North Korea to squeeze them until they collapse. If we don't succeed, we shall surely all fall down. Don't say North Korea didn't warn us.
