Thirty-eight people were killed and 65 injured in two suicide bombings at two Metro stations here on Monday.
The bombings occurred during the morning rush hours on Moscow Metro's oldest Red Line.
The first bomb, equivalent to 4 kg of TNT, ripped through a carriage when a train stopped at the Lubyanka station, killing 26 passengers. Within 45 minutes, a less powerful bomb went off in a train as it pulled up at the Park Kultury station, just three stations away from Lubyanka, killing 12 people.
The victims included three foreigners – a national of the Philippines and two Malaysians. The home-made belt bombs were stuffed with nuts and bolts to cause more casualties.
Head of Russia's Federal Security Service (FSB) Alexander Bortnikov said available evidence pointed to terrorists operating in North Caucasus, which includes the restive Chechnya.
Investigators said the attacks appeared to have been well coordinated. Closed-circuit TV in the stations captured the faces of the suicide bombers and their accomplices. Police sent out the portrait of a bearded man and two women wanted in connection with the attacks.
President Dmitry Medvedev ordered stepped up security on transport across the country and vowed to fight terrorism “without hesitation, to the end.”
A security official said the bombings could have been staged in retaliation to recent killings of several terrorist leaders in North Caucasus.
He pointed out that the Lubyanka Station is situated underneath the headquarters of the FSB, successor to the Soviet-era KGB.
In February, Chechen rebel leader Doku Umarov warned in an interview on a rebel website that “the zone of military operations will be extended to the territory of Russia ... the war is coming to their cities.”
He claimed responsibility for the bombing of an express passenger train that killed 26 people en route from Moscow to St. Petersburg.
On Tuesday, Moscow will mark a day of mourning for the victims of the Metro bombings.