SEOUL (Reuters) – An activist group in South Korea said on Thursday it had flown balloons into North Korea carrying leaflets criticising leader Kim Jong Un, just days after Pyongyang sent thousands of balloons carrying trash in the other direction over the border.

Park Sang-hak, a defector who fled North Korea in 2000, said his group, Fighters For Free North Korea, had launched 10 balloons from the border town of Pocheon with 200,000 flyers, 5,000 USB sticks containing K-pop videos and dramas, and 2,000 $1 notes.

North Korean defectors and activists in South Korea have for decades released balloons carrying anti-Pyongyang leaflets and aid parcels across the heavily fortified frontier.

Park’s latest campaign came after North Korea recently said it had sent 3,500 balloons carrying 15 tons of trash into the south. The balloons, in some cases also carrying excrement, sparked tension in border towns and prompted Seoul to suspend a 2018 inter-Korean military pact and resume military activities around the border.

Images provided by Park showed one leaflet consisting of a photograph of Kim and his sister with a note reading: “The enemy of the people Kim Jong Un sent filth and trash to the people of the Republic of Korea, but we defectors send truth and love to our North Korean compatriots,” using the South’s official name.

Other images showed Park and his colleagues holding balloons carrying packages at night.

“Kim Jong Un has inflicted the worst insult and humiliation on 50 million of our people,” the group said in a statement, referring to the trash balloons and vowing to continue sending leaflets until Kim apologised.

South Korean President Yoon Suk Yeol, in his Memorial Day speech on Thursday, reaffirmed his pledge to build peace through strength, which he said would help transform the North, restore its peoples’ freedom and human rights, and ultimately achieve unification.

The two Koreas are still technically at war after their 1950-53 war ended in an armistice, not a peace treaty, and the North has long denounced defectors as “human scum”.

After Seoul warned of restarting blaring loudspeakers along the border after a six-year letup, Pyongyang said it would stop sending trash balloons but pledged to resume the practice if anti-North leaflets arrived again.

South Korea’s government said on Wednesday it was monitoring the issue of sending leaflets over the border, though noted that the practice was protected by a ruling on freedom of speech.

(Reporting by Hyonhee Shin; Editing by Ed Davies and Gerry Doyle)