Zagreb (AFP) – A Croatian court sentenced a 20-year-old to the maximum 50 years in prison for stabbing a seven-year-old pupil to death at a school in December last year and wounding four other people.

The attacker was a former pupil of the school in a suburb of the Croatian capital Zagreb.

He entered during class time and stabbed a teacher and several children, the indictment said.

One child was killed and three children and the teacher were injured.

"This constitutes one count of aggravated murder of a child, along with four counts of attempted aggravated murder and a total of 50 criminal offences involving violations of children's rights," said Kresimir Devcic, a spokesperson for the Zagreb court.

The unprecedented attack deeply shocked and angered the country, prompting protests in the days that followed calling for safer schools.

"The court panel considers that only the harshest sentence -- 50 years in prison -- can achieve both special and general prevention," Devcic added.

He said the perpetrator was tried as an adult, and that a psychiatric assessment of criminal responsibility had been carried out.

The convicted man was arrested immediately after the attack and has remained in custody since.

The maximum sentence of 50 years in prison is rarely handed down by Croatian courts. The ruling can be appealed.