North Korea sent hundreds of balloons carrying cigarette butts and other trash over the border late Saturday, triggering public safety alerts across the capital area and leading South Korea to threaten to respond with “unendurable measures.”

The weekend balloon blitz follows a statement from the South Korean government warning North Korea of consequences should Pyongyang conduct such launches. North Korea flew some 260 balloons south of the border mid-last week carrying feces and other waste.

South Korea’s Joint Chiefs of Staff (JCS) said in a statement that as of 1 p.m. KST on Sunday, around 720 balloons carrying cigarette butts,