At least three people were killed in a northwestern Bosnian town Wednesday when a school employee opened fire on his colleagues.

The shooting took place around 10 a.m. local time in a secondary school building in Sanski Most, about 300 kilometers (180 miles) northwest of Bosnia’s capital, Sarajevo, said regional police spokesman Adnan Beganovic.

Beganovic told The Associated Press that the man used a "military weapon, an automatic rifle." He then attempted to kill himself and is in serious condition in a hospital in nearby Banja Luka.

The victims include the school principal, a secretary and a teacher, said Beganovic.

Regional N1 television reported that the man had a dispute with the school management. No other details were immediately available.

Bosnian schools are closed for the summer holiday but Beganovic said there were people in the school as repeat examinations were underway.

The Balkan region is awash with small arms and weapons since the 1990s wars, part of the breakup of Yugoslavia, particularly in Bosnia, a country of about 3.5 million people.

According to a 2010 study by the United Nations Development Program, there were about 750,000 weapons in illegal possession in Bosnia.