(CNN) Twenty people -- most of them teenagers -- are now confirmed dead after a student went on a shooting spree and detonated a bomb at a college in Crimea, state-run Russian news agency TASS reported Thursday.

The suspected perpetrator also "shot himself dead" after the attack, said Crimean government head Sergey Aksyonov. The Crimean leader announced on Wednesday there would be three days of mourning.

The site of the attack at a college in the Crimean city of Kerch.

Crimea -- a peninsula surrounded by the Black Sea and the Sea of Azov -- was annexed by Russia from Ukraine in 2014.

Russia's National Anti-Terrorism Committee told CNN that the blast was caused by an "unidentified explosive device" at a college in the city of Kerch -- where a new 19-kilometer bridge links Crimea to Russia.

Russia's Investigative Committee said in a statement: "According to preliminary data, an unidentified explosive device packed with metal objects went off today in the dining room of the Kerch Polytechnic College."

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