A seven-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. A local hospital said the wounded teacher had life-threatening injuries, Reuters reports.

Officials said the attack took place at 9:50 a.m. local time at the Prečko Elementary School in the village of the same name. They described the attacker as a “young man” and said that he had been taken into custody.

The Croatian Ministry of the Interior announced that the attacker was 19 years old. Local media reported that the attacker was a former student of the school and showed video footage of children fleeing the school building and a medical helicopter landing in the school yard.

Croatian Prime Minister Andrej Plenković said he was “horrified” by the attack and that the authorities were still working to determine what exactly happened. He said that several children were taken to various hospitals in Zagreb.

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

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