"Bomb specialists continue to work at the location of the incident. So far, no signs of explosives have been found," the FSB spokesman said.
The deputy prosecutor of the Arkhangelsk Region, Yury Shperling, said that investigators believe that the explosion was a result of a natural gas explosion in one of the apartments.
Rescue workers from Moscow have started to work on the ruins. "Presently, dog handlers are searching the ruins with specially trained dogs that find places where people may be still trapped," Viktor Beltsov, a spokesman for the Emergencies Ministry's information department, reported.
According to him, rescue workers are searching for people, who are still alive.
Seventy-six rescue workers from the Tsentrospas and Leader Groups and four dogs have arrived in Arkhangelsk from Moscow. Members of the Arkhangelsk and North Dvina Rescue Services are also working at the site.
According to the Emergencies Ministry, the explosion killed five people and 20 people have been rescued. Fourteen of the 20 people have been hospitalized.