A Unification Ministry official is said to have asked a civic group to cancel its plan to fly anti-North Korea leaflets across the border in balloons.

The official on Tuesday made the demand in a meeting with Park Sang-hak, president of the civic group Fighters for Free North Korea (FFNK), saying that the government cannot approve the group’s public leaflet campaign due to safety concerns for residents in the border area.

Park is known to have responded that he would push for the plan if the North fails to offer an apology for the Cheonan incident by Thursday, the fifth anniversary of the North’s deadly sinking of the South Korean naval ship.

The group and some other civic groups announced Monday that they would temporarily suspend the plan to fly anti-North Korea leaflets and copies of the movie “The Interview” until Thursday, demanding an apology from the North.