A 7-year-old girl was killed and at least five other students and a teacher were wounded in a knife attack at a school in the Croatian capital, Zagreb, on Friday, police said. The local hospital said the wounded teacher had suffered life-threatening injuries, Reuters reported.

Officials said the attack happened at 9:50 a.m. local time at the Precko Elementary School in the neighborhood of the same name. They described the attacker as a “young male” and said he had been detained.

Croatia’s Interior Ministry said the attacker was 19 years old. Local media reported the attacker was a former student at the school, and showed video footage of children running away from the school building and a medical helicopter landing in the schoolyard.

Croatian Prime Minister Andrej Plenkovic said he was “appalled” by the attack, and that authorities are still working to determine exactly what happened. He said several children have been taken to various hospitals in Zagreb.

State television reported the attacker went straight into the first classroom he found after entering the school, where he attacked the students and their teacher.

School attacks are rare in Croatia. Last May, a teenager in neighboring Serbia opened fire at a school in the capital Belgrade, killing nine fellow students and a school guard.