COPENHAGEN, Denmark (AP) — Danish police have begun to carry out border checks at its crossings with Sweden after a series of shootings and explosions around Copenhagen that Danish authorities say were carried out by people from Sweden.

Police spokesman Jens Jespersen told The Associated Press on Tuesday that at checks on the Oresund Bridge between Copenhagen and the Swedish city of Malmo, officers have "a particular focus on cross-border crime involving explosives, weapons and drugs." He also says authorities are stopping cars to have "a peak at who is inside."

The controls are also being carried out at ferry ports.

They follow 13 explosions in Copenhagen since February. A June shooting in the city killed two Swedish citizens. Also, a shooting Saturday in Malmo killed a 15-year-old boy and critically wounded another teenager.