Three staff members of a high school in the western Bosnian town of Sanski Most were killed on Wednesday when a school employee shot them.
Police were notified at 10:15 AM (0815 GMT) that a man had opened fire at the school with an automatic rifle, the police spokesman for Una-sana canton, Adnan Beganovic, said, adding that the shooter killed the school dean, the secretary and a teacher.
"The suspect tried to take his own life and was gravely injured," Beganovic said. He was transferred for emergency treatment in the nearby town of Banja Luka. An investigation is underway.
The school had not yet reopened from the summer holidays so no children were involved.
N1 TV, citing witnesses, said that a janitor who had a history of disagreements with the management and was under disciplinary proceedings, sought out specific people and shot them. Reuters could not immeditely verify that report.
Mass shootings are comparatively rare in the Western Balkans which is awash with weapons that remained in private hands from wars in the 1990s.
In July, a war veteran in neighbouring Croatia shot five people including his mother in a nursing home and wounded six others.
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Russia launched a "massive" drone attack on Ukraine's central Cherkasy region, injuring six people and triggering a blackout in part of Cherkasy city, the local governor said on Thursday.
The United Nations and aid groups have warned on Wednesday that humanitarian operations in the Palestinian territories, particularly Gaza, were at risk of collapse if Israel does not lift impediments that include a "vague, arbitrary, and highly politicised" registration process.