Moscow: One person was killed and three injured when an explosive device went off inside a building housing the FSB security service in Arkhangelsk in northern Russia, an official said.
The device went off just before 9 am (0600 GMT) in the FSB building in the centre of the city, more than 1,000 kilometres north of Moscow, Artyom Botygin, a spokesman for the regional governor told AFP.
"One person was killed and three others were hospitalised," he said.
Regional governor Igor Orlov said it was too early to say whether this was a suicide bombing.
"Things are very serious," he said in comments confirmed by his spokesman to AFP.
Orlov added that authorities were working to establish the identity of the dead person and the type of the explosive device.
"We are taking measures to increase security of all public and state buildings in Arkhangelsk region."
A FSB representative for the Arkhangelsk region confirmed the explosion to AFP but declined to provide further details.
The governor also inspected the scene and security services convened an emergency meeting.