Belgrade school shooting: At least 9 dead after teen opens fire

At least nine people are dead and seven others are wounded after a shooting at a school in Serbia's capital on Wednesday, authorities said.

The suspect, who has been arrested, is a 13-year-old boy who allegedly took his father's gun to the Vladislav Ribnikar school in central Belgrade and opened fire, according to police.

Eight students -- all children -- and a security guard were among those killed. Six other students as well as a teacher were injured and taken to a local hospital, police said.

Investigators believe the suspect had been planning the attack for a month, according to police.

The teenager allegedly drew a map of the school and wrote a list of students he intended to target, police said.

ABC News' Joe Simonetti contributed to this report