A high-profile defector activist says he launched 20 balloons carrying anti-regime leaflets and South Korean music toward North Korea on Thursday night, prompting the DPRK leader’s sister Kim Yo Jong to threaten retaliatory measures after tit-for-tat balloon launches in recent weeks.

Park Sang-hak, the head of Fighters for a Free North Korea (FFNK), said in a statement that the activist group launched the balloons in response to the DPRK’s launches of trash-carrying balloons since last month and Russian leader Vladimir Putin’s state visit to Pyongyang this week.