An FSB spokesperson told journalists that "according to preliminary information, both blasts were carried out by female suicide bombers," who brought explosives onto crowded Metro carriages and set them off in what appears to have been a carefully planned and coordinated series of attacks.
President Dmitri Medvedev pledged to step up security in the Russian capital and to expand the security crackdown in the turbulent north Caucasus, which is the almost certain source of the threat.
"We will continue the operation against terrorists without hesitation and to the end," Mr. Medvedev said in televised remarks after the tragedy. "It is difficult to prevent such terrorist attacks and to provide security on transport," such as Moscow's sprawling and overcrowded Metro system, he said.
"It is necessary to tighten what we do, to look at the problem on a national scale, not only relating to a certain populated area but on a national scale. Obviously, what we have done before is not enough," he added.
Security experts offer cautious praise for Russian authorities who appear to have avoided mass panic with a quick and competent response that contrasts sharply with clumsy reactions to previous terrorist strikes in downtown Moscow early in the past decade. The areas were quickly cordoned off by police and thousands of shaken and frightened survivors evacuated from the stations – which are among the deepest in the city – in an orderly fashion, and helicopters were brought into the paralyzed city center to extricate the wounded.