North Korea has threatened to reduce South Korea to rubble unless it stops what the North calls a policy of confrontation.
The harsh attack came after citizens from the South sent anti-government leaflets over the North in balloons.
The latest leaflets made allegations about the North's leader, Kim Jong-il.
Speculation about the leader's health has been rife since he failed to appear at a series of nation-praising events in recent months.
"The puppet authorities had better bear in mind that the advanced pre-emptive strike of our own style will reduce everything ... to debris, not just setting them on fire," the North's military said in a statement to the official KCNA news agency.
"It will turn out to be a just war... to build an independent reunified state on it," it added.
Military representatives from the North and the South held a rare scheduled meeting on Monday, at which the North complained directly about the leaflets.
Analysts say the North refrained from bellicose military threats while it was receiving regular aid from the South.
But the current government in Seoul, led by President Lee Myung-back, has been taking a harder line, amid questions over whether the South's so-called "Sunshine Policy" of engagement with the North was working.
President Lee has advocated tying aid to progress on the North's nuclear disarmament.
The South says the leaflet campaigns are nothing to do with the government.
But the North's military statement said the acts of non-government organisations were "nothing but premeditated operations" against the North.
Many batches of leaflets have been sent from the South over the years.
Activists had recently sent a new batch of tens of thousands of leaflets, attached to balloons, despite warnings from Seoul not to do so.
The leaflets were printed in waterproof ink on plastic sheets and carried the names of South Korean civilians and prisoners of war believed to be held in the North, as well as a family tree said to chart Kim Jong-il's relationships with several women who bore him children.
A North Korean defector now leading the leaflet campaign in the South, Pak Sang-hak, has reportedly said he has no plans to stop sending the airborne messages.
US and South Korean officials say Mr Kim may have fallen seriously ill in August, raising questions about leadership and also about who is making decisions about the country's nuclear weapons ambitions.