A top North Korean official on Friday warned that the country would soon take “painful” retaliation against South Korea, saying that its trust in Seoul to uphold inter-Korean agreements has been “shattered” by the government’s failure to stop activists from sending anti-regime leaflets into its territory.

In a statement carried by the Korean Central News Agency (KCNA) ahead of Monday’s 20th anniversary of the first inter-Korean summit, Pyongyang dismissed Seoul’s efforts to stop NGOs from launching balloons and bottles carrying anti-DPRK literature as “lip-service.”

“The times ahead will be truly regrettable and painful for the South Korean authorities,” the statement,