Croatian police said that a 7-year-old girl was killed and 6 others were injured in a stabbing attack at a school in Croatia.

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

Officials said the attack occurred at 9:50 a.m. local time at Brico Elementary School in the neighborhood of the same name. They described the attacker as a “young man” and said he had been arrested.

The Croatian Interior Ministry said the attacker was 19 years old. Local media reported that the attacker was a former student at the school, and showed video clips of children escaping from the school building and a medical helicopter landing in the school yard.

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

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

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