(CNN) -- Police in Finland say they have arrested more than 20 men on charges related to the sexual abuse of children. The men are suspected of using the Internet to approach girls between the ages of 9 and 15, engage them in sexual discussions and, in some cases, to meet for sex in exchange for money, cigarettes or alcohol, the National Bureau of Investigations said in a statement. The men acted alone, police said. It was not clear when the arrests were made. The agency's statement did not say and police officials were not in the office to comment Thursday afternoon. At least one of the men, who range in age from 22 to 48, has a history of similar crimes against children, the agency said. Three of those arrested have already been convicted and sentenced to prison, according to the statement. CNN's Per Nyberg contributed to this report.
Police in Finland arrest more than 20 on charges related to child sex abuse . The arrests began with a single incident in 2011, police say . At least one of the arrested has a history of similar crimes against children .