At least 37 people were killed and 33 wounded on Monday when suicide bombers detonated explosives on two packed Moscow metro trains during the morning rush hour.

This is the worst attack in the Russian capital for six years, officials said. No group immediately claimed responsibility for the blasts but suspicion was likely to fall on groups from Russia's North Caucasus, where the Kremlin is fighting a growing Islamist insurgency.   

The first blast just before 8 am (0400 GMT) tore through the second carriage of a train as it stood at the Lubyanka metro station, close to the headquarters of Russia's main domestic security service FSB. It killed at least 23 people.

Another blast about 40 minutes later wrecked the second carriage of a train waiting at the Park Kultury metro station, killing 14 more people.

"Two female terrorist suicide bombers carried out these bombings," Moscow Mayor Yuri Luzhkov told reporters at Park Kultury metro station.

Surveillance camera footage posted on the Internet showed motionless bodies lying in Lubyanka station lobby and emergency workers treating victims.   

The Russian rouble fell to 34.25 from 34.13 against the central bank's euro-dollar basket. Russian equity markets opened down 0.15 percent.

Russian prosecutors said they had opened an investigation.
Russian Prime Minister Vladimir Putin was being updated regularly on developments, a spokesman said.

The current death toll makes it the worst attack on Moscow since February 2004, when a suicide bombing killed at least 39 people and wounded more than 100 on a metro train. Chechen separatists were blamed for that attack. - Reuters