South Korea is accusing rival North Korea of floating propaganda leaflets via a river in the first such incident.

The Defense Ministry said Wednesday it recently discovered dozens of plastic bags, each carrying about 20 leaflets, near a Seoul river close to the tense Korean border. Seoul is only an hour's drive from the border.

It says the leaflets contained threats to launch missile attacks on South Korea and praises of the North's political system.

A Cold War-style standoff flared after the North's fourth nuclear test in January.

Seoul resumed blasting anti-Pyongyang propaganda broadcasts and K-pop songs from border loudspeakers. Pyongyang responded by restarting its own border broadcasts and floating balloons carrying anti-South leaflets.

The ministry says it's the first time for Pyongyang to use a river to send leaflets.