The Russian special service has been cooperating with U.S. partners in the investigation of the Boston bombings, President Vladimir Putin said Saturday.

Interaction of special services between the two sides has been arranged "considering that some people possessing valuable information and the criminals' relatives are in Russia," Putin said in an interview with a local TV channel.

Any terrorist attack and murder is a heinous crime, Putin said, adding Russia immediately extended its condolences to the U.S. side following the fatal attack.

The two brothers of Chechen origin detonated two home-made bombs near the finish line of the Boston Marathon last Monday, killing three people and injuring more than 200 others.

Tamerlan was killed in a shootout with police, while Dzhokhar was detained last Friday after a massive manhunt that paralyzed the city of Boston.