North Caucasus terrorist groups are possibly involved in the Moscow subway bomb blasts that killed 37 and injured at least 65 people, the Federal Security Service chief said on Monday.

"According to preliminary information, these terrorist acts were committed by terrorist groups related to the North Caucasus region. We'll consider it as the basic version because the bodies of two female suicide bombers who were residing in the North Caucasus have been found [at the explosion sites]," Alexander Bortnikov said.

The blasts occurred in the Moscow Lubyanka and Park Kultury stations on the Sokolnicheskaya subway line on Monday morning.

The blasts, described by a police source as "a well-planned terrorist attack," took place in crowded trains as people hurried to work on the first day of the working week.

Bortnikov also said work was under way to define the group of persons involved in carrying out the bomb attacks as well as preventing possible provocations.

MOSCOW, March 29 (RIA Novosti)