The activists launched balloons carrying about 200,000 anti-North Korea leaflets and one-dollar bills over the border on Monday, the 66th anniversary of the founding of the North Korean ruling Workers’ Party.

North Korea warned over the weekend that it would fire at South Korea if leaflets were launched on the anniversary. The North has issued similar threats against leafletting in recent years.

South Korean activists say they won’t yield to the North’s threats, and continue leafletting to urge North Koreans to rise up against the authoritarian government.