They did literally say they would do this a week ago

“Tit-for-tat action will be also taken against frequent scattering of leaflets and other rubbish by the Republic of Korea near border areas. Mounds of wastepaper and filth will soon be scattered over the border areas and the interior of the Republic of Korea and it will directly experience how much effort is required to remove them.”

http://www.vok.rep.kp/index.php/detail_com/comde/ien240526001/48/en

Lol