A blast outside an underground station in central Moscow that killed ten people was caused by a female suicide bomber, according to the federal security service FSB.

The mighty explosion was caused by a substance of 1 kg trotile explosive.

Earlier the interior ministry had announced several theories were being considered, among them a suicide bomber but also an explosion in a car parked outside the station.

The explosion ripped off at about 8 pm local time on Tuesday when reportedly two cars were set on fire outside the central Rizhskaya station of the Moscow tube. It was later known that one car exploded and the other one was grabbed by the fire.

More than 50 people, including four children, were rushed to hospitals, some dozen of them with serious injuries following the deadly blasts.

The Brigadiers of Islambuli later claimed responsibility for the explosion in a notice posted on an Islamist web site. The same militant grouping announced last week their kamikazes acrried out the blasts that downed two Russian planes.

The explosion came just a week after twin bombings brought down two airliners killing all 90 people aboard, in attacks authorities blamed on Chechen terrorists.

According to a journalistic research by Russian Izvestia daily, two days ahead of the crashes two Chechen females believed to have committed suicidal bombing on board of the planes had arrived in Moscow.

Amnat Nagaeva and Satsiva Djebirhanova were accompanied by another two women, the sister of the former Roza Nagaeva, and Mariam Taburova.

Approached by the daily's reporters, their relatives ruled out any possibilities for the four women being linked to any terrorist activities, pointing out the lack of any motives for such.