The twin blasts that rocked central Moscow's subway stations during the rush hour early Monday were triggered by plastic-based explosives, said a spokesman for the Investigative Committee of Russian Prosecutor General's Office.

Citing preliminary investigation, Vladimir Markin told reporters that two explosions were set off by two female suicide bombers with shell-less explosive devices equivalent to 3 kg TNT.

Currently no groups have claimed responsibility for the blasts, and "the only thing we can say for sure (is that) the woman from the Culture Park station had black hair," said Markin as quoted by the Itar-Tass news agency.

Head of the State Duma Security Committee Vladimir Vasilyev said terrorists from North Caucasus had probably launched the attack, as a retaliation against the recent serial special operations conducted by Russian law enforcement in the region.

Following the catastrophe, Russian President Dmitry Medvedev vowed the continuation of suppressing terrorism at an urgent meeting on the occasion.

"The suppression of terrorism will continue. We will carry out uncompromising operations against terrorists to the end," said the president as quoted by the Interfax news agency.

Medvedev also instructed the government to provide full aid to families of the metro victims.

Russian Emergency Situations Ministry said at least 35 people were killed in the twin blasts.