A shooter killed eight people and wounded at 13 in an attack that took place Thursday evening near the capital of Belgrade, just a day after the mass killing in a Belgrade elementary school.

The 21-year-old male attacker, identified by his initials as U.B., first opened fire in the village of Dubona, and then in the villages of Malo Orasje and Sepsin near the town of Mladenovac, some 50 kilometers south of Belgrade.

An off-duty police officer and his sister were among those killed, while the youngest victim was born in 2008.

The N1 portal was told that this was most probably a terrorist act.

All special police units are on the ground, including the Special Antiterrorist Unit (SAJ), the Gendarmerie and helicopter units.

The Serbian state TV (RTS) reported that the shooter was arrested Friday morning near the city of Kragujevac.