Twenty people were killed and dozens more were wounded in a deadly bomb and gun attack in a college by a student in Crimea on Wednesday, a top official in Crimea said.

There was only one perpetrator, but multiple accomplices are believed to have been involved in the preparation, said Sergei Aksyonov, the regional leader in Crimea.

Security measures have been strengthened in all major facilities and departments in the city of Kerch, Crimea, and the place where the explosion occurred is still on alert.