South Korean police said Tuesday that they’ve summoned two activists accused of raising tensions with North Korea by sending propaganda balloons or plastic bottles filled with rice across the border. Park Sang-hak, a North Korean refugee who has floated anti-Pyongyang leaflets by balloon across the land border, and his brother Park Jung-oh, who has floated plastic bottles filled with rice across the sea boundary, were being questioned at the Seoul Metropolitan Police Agency, an agency officer with direct knowledge of the cases said.