Nine people were reported dead on Wednesday in a school shooting in Serbia.
A 13-year-old pupil at Belgrade's Vladislav Ribnikar Elementary School is suspected of carrying out the attack.
The boy, identified as Kosta Kecmanovic, was arrested on school grounds, Serbia's Ministry of Internal Affairs said.
The ministry said eight children and a security guard were killed.
Six children as well as a teacher were injured in the attack at the school, it said.
A local official told journalists the guard was killed and the teacher seriously wounded as they tried to protect pupils.
The guard “wanted to prevent the tragedy and he was the first victim”, said Milan Nedeljkovic, president of the local government district in Belgrade.
“Probably the tragedy would be even bigger if the man did not stand in front of the boy who was shooting.”
Belgrade Police Chief Veselin Milic identified the dead pupils as seven girls and one boy, born between 2009 and 2011.
Chief Milic said the gunman had made weeks-long preparations for the attack, including sketching classrooms and making a list of targets.
The motive for the shooting was not clear.
Police at the scene were “intensively working to shed light on all the facts and circumstances that led to this tragedy”, the interior ministry said.
Education Minister Branko Ruzic was quick to blame “the cancerous, pernicious influence of the internet, video games, so-called western values”. Serbia is an aspiring EU member but has various quarrels with the bloc and western powers.
The EU's foreign policy chief Josep Borrell offered “deep condolences to the families and close ones of the victims”.
The assailant called the police himself when the attack was over, though authorities received a call reporting the shooting two minutes earlier, officials said.
Footage on local TV showed a commotion outside the school as police took the suspect, whose head was covered, to a car parked in the street.
There were doubts over whether the boy would be subject to criminal proceedings because of his age.
Interior Minister Bratislav Gasic said the weapons were licensed and kept in a safe but the boy apparently knew the code. His father was also arrested.
Mass shootings are rare in Serbia, which has strict gun laws, but many weapons remain unregistered after the wars and unrest of the 1990s.
Authorities declared three days of nationwide mourning starting on Friday. Schools across Belgrade were closed following the shooting, according to state media.
