A North Korean defectors’ group claimed it carried out a controversial anti-Pyongyang leaflet campaign despite deepening inter-Korean tension over the movement. 

Park Sang-hak, head of Fighters for a Free North Korea, said on Tuesday that 500-thousand leaflets were disseminated across the border Monday night between 11 p.m. and midnight. Park added that they chose “shady places” in Deogeun-ri, Paju City, Gyeonggi Province to evade police.

The defector-turned-activist announced last week that they would send a million leaflets to the North around the 70th anniversary of the outbreak of the Korean War. 

In addition, 500 booklets, two-thousand one dollar bills and one-thousand memory drives were also sent, attached to helium-filled balloons as police confiscated the hydrogen gas belonging to the group. 

Park said he trained six novice members to send the materials as he is being monitored. South Korean police and the military said they are seeking to confirm his claims. 

The alleged campaign came despite Seoul’s efforts to deter them as Pyongyang increases threats over them. Police have been investigating the group after the Unification Ministry filed a criminal complaint against two defectors’ groups, including Park’s, for violating regulations on inter-Korean exchanges.