North Korea sent some 600 balloons carrying trash into South Korea overnight, Seoul said on Sunday, in Pyongyang’s latest move to rile its rival neighbour. The balloons carrying garbage such as cigarette butts, cloth, paper waste and plastic were found across the capital from 8 p.m. to 10 a.m. (1100 GMT on Saturday to 0100 GMT on Sunday), South Korea’s Joint Chiefs of Staff said.

It said the military was monitoring the starting point and conducting aerial reconnaissance to track down and collect the balloons, which have large bags of trash suspended beneath them.

North Korea on Wednesday sent hundreds of balloons carrying trash and excrement across the heavily fortified border as what it called “gifts of sincerity”. Seoul responded angrily, calling the move base and dangerous.

South Korea’s Defence Minister Shin Won-sik said during a meeting with U.S. Defence Secretary Austin Lloyd on the sidelines of the Shangri-La security dialogue in Singapore on Sunday that the balloons violated the armistice agreement, according to South Korea’s military.

The two reaffirmed a coordinated response to any North Korean threats and provocations based on the South Korea-U.S. alliance’s combined defence posture, it added. Emergency alerts were issued in North Gyeongsang and Gangwon provinces and some parts of Seoul on Sunday, urging people not to come into contact with the balloons and to alert police. South Korea’s National Security Council standing committee will meet on Sunday afternoon to discuss whether to resume blasting loudspeakers at North Korea in response to the trash balloons, Yonhap news agency reported, citing the presidential office.

South Korea stopped blaring propaganda across the border in 2018 after a rare summit with North Korean leader Kim Jong Un.