North Korea claimed Friday the scattering of anti-Pyongyang leaflets is tantamount to a "declaration of war," as South Korean conservative activists planned to send 100,000 leaflets across the border this weekend.

It also represents a grave breach of international law, the North said in a white paper published by its state institute on reunification.

"It's a de-facto declaration of war to insult and slander our supreme self-dignity and system with every kind of false and fabricated information," it said.

The North has ratcheted up criticism of the leaflet campaign, urging the South's government to take forcible measures to block it.

The South has maintained that it has no legal grounds for interfering in the civilian-led move.

On Thursday, an organ of the powerful Workers' Party of Korea also issued a statement sharply criticizing the South's government and activists.

The Committee for the Peaceful Reunification of the Fatherland warned Pyongyang would take further military countermeasures against the leaflet spread.

Earlier this month, the North opened fire at leaflet-carrying balloons flown by activists near the border.

Another group of activists said they would send 100,000 leaflets into the North from a border area on Saturday.

Some activists' groups, largely led by North Korean defectors, use large balloons to send leaflets critical of the communist nation's leaders and system as well as radios, DVDs and one-dollar bills. (Yonhap)