Russia said it had launched a probe into terrorism after a 17-year-old blew himself up at a regional headquarters of the FSB security service yesterday, wounding three employees.
The bomber took an explosive device into the FSB building in the northern city of Arkhangelsk and a blast occurred inside the entrance just before 9:00am (0600 GMT), the National Anti-Terror Committee said. The bomber, identified as a 17-year-old local resident, died, it added.
Authorities have cordoned off streets around the building, with police and experts combing the area for clues.
Attacks on police and security services are common in Russia's restive Northern Caucasus but are very rare in the rest of the country.
Investigators said they opened a probe into terrorism and illegal possession of ammunition.
Three FSB employees were hospitalised with various injuries after the blast in the city, which is located more than 1,000 kilometres (800 miles) north of Moscow, the committee said in a statement.
President Vladimir Putin -- himself a former FSB officer -- was informed about the explosion, his spokesman Dmitry Peskov told reporters but declined to speculate on the cause.