Czech police say an international law enforcement team has broken up a gang that allegedly produced amphetamines to distribute on the black market in Sweden.

Police said Wednesday that seven suspected members of the group have been arrested in a joint operation by Czech, Swedish and Hungarian forces. The alleged boss, a Swede of Serbian origin, and two other Swedish nationals of Czech and Hungarian origins, were arrested in Malmo, Sweden.

Four Czech suspects were arrested in the Czech Republic.

A police statement said the ring was estimated to have produced 3.5 metric tons (3.9 tons) of amphetamines in the last five years, enough to meet the demand in Sweden.

Police say the lab they discovered was the first illegal amphetamine production facility found on Czech territory.