North Korea released a new booklet Wednesday repeating claims that Seoul intentionally introduced COVID-19 to the country, in what one expert called a propaganda effort seeking to foster opposition to anti-regime leafleting among the South Korean public.

The 31-page Korean-language booklet, titled “The Root of the Problem,” takes aim at defectors who send leaflets and specifically condemns high-profile activist Park Sang-hak, labeling leaflets “psychological warfare” and a “prelude to a serious invasion of North Korea.”