Pyongyang on Tuesday blew up deeply symbolic roads and railways connecting the two Koreas after warning any further drone flights would be considered a declaration of war, and ordered soldiers on the border to prepare to fire.

“Millions of young people have turned out in the nationwide struggle to wipe out the ROK scum who committed a serious provocation of violating the sovereignty of the DPRK through a drone infiltration*,” the official Korean Central News Agency said, referring to both countries by their official acronyms. It said more than 1.4 million youth league officials and youth and students across the country volunteered to join or rejoin the Korean People’s Army on October 14 and 15.

South Korean authorities in areas near the border with the nuclear-armed North are moving to prevent activists from launching balloons. To protect its citizens, the provincial government of Gyeonggi will designate Yeoncheon, Gimpo and Paju “*as special ‘danger’ zones where anyone trying to send leaflets to the North may be subject to criminal investigation”, an officer from the Gyeonggi provincial goverment told AFP.

South Korean activists – many are former North Koreans who defected – have also sent materials such as USB drives containing K-pop tracks and K-dramas. The isolated North is extremely sensitive about its people gaining access to the South’s popular culture.

Since late July, Pyongyang has broadcast eerie sounds along the border – some resembling the cries of wild animals – in apparent retaliation. “The anxiety and suffering of residents in border areas is becoming increasingly severe,” the Gyeonggi province said in the statement. “Many are reporting that they can’t sleep without medication due to the constant influx of garbage balloons and unsettling broadcasts from the North.”