At least one person was killed and three others injured after an unknown explosive device went off Wednesday at the entrance of the Russian Federal Security Service (FSB) building in the northwestern city of Arkhangelsk, the region's governor, Igor Orlov said.

The crime was committed inside the building and it is too early to draw conclusions, Orlov said.

Security has been tightened in public areas of the city as the type of the explosive device is being identified, he said.