Serbian authorities say a psychologically disturbed police officer went on a shooting rampage Tuesday, killing four colleagues and seriously wounding three others in the southeastern city of Nis.

The officer, identified as Vladimir Rovcanin - a Serb from Kosovo - opened fire at the Nis headquarters of the Serbian Security Information Agency, where he worked. Officials later subdued and arrested him.

Among the dead was one woman.

Serbia's interior minister, Dusan Mihajlovic, called the shooting a "tragedy." He said it should serve as a warning that people who saw combat in Kosovo sometimes suffer from the so-called "Vietnam syndrome," causing them to commit terrible crimes for no apparent reason.