The attack at the Kerch Polytechnic College wounded around 50 in the city of Kerch, near the eastern end of the peninsula that Russian Federation annexed from Ukraine in 2014, the Investigative Committee said. The committee also said he might not have been acting alone and it was looking for other possible participants.
A committee spokeswoman said the death toll had risen to 13 after initial reports 10 people were killed in the explosion that detonated at around noon. Most of the victims were students.
Law enforcement officials initially said they were treating the incident at Kerch Polytechnic College as a terror attack, but later said it was mass murder.
The committee said all the victims died of gunshot wounds.
Witnesses did not speak of an explosion but said one or more armed men attacked the school.More news: Key Democratic senator says Saudi response on Khashoggi 'strains any credibility'
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"After that they were running all across the second floor, opening the doors of classrooms and shooting everyone they found there".
"The President has instructed the Ministry of Health and Emergency Services Ministry to take emergency measures to assist victims of this explosion, if necessary, to ensure the urgent transportation of seriously wounded patients to leading medical institutions of Russian Federation, whether in Moscow or other cities", Peskov said.
The wars were followed by an Islamist insurgency in the North Caucasus region, east of Crimea, and insurgents have claimed responsibility or been blamed for most of the bombings and other attacks in Russian Federation over the years.
TASS news agency cited Sergei Melikov, the first deputy head of the Russian National Guard, as saying the explosion was an act of terrorism carried out using a homemade bomb. They burst in five or 10 minutes after I'd left.
"There are already lots of people in the emergency room, and in the operating theatre", an employee of the nearest hospital said.