Two female suicide bombers are believed to have caused explosions on two packed Moscow metro trains during this morning's rush hour, killing at least 37 people.
The bombing was the worst attack in the Russian capital for six years, and the deal toll is expected to rise, officials said. Another 33 were wounded.
No group immediately took responsibility for the blasts but suspicion is likely to fall on groups from Russia's North Caucasus, where the Kremlin is fighting a growing Islamist insurgency.
The first blast just before 8am tore through the second carriage of a train as it stood at the Lubyanka metro station, near the headquarters of Russia's main domestic security service (FSB). It killed at least 23.
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 said. Surveillance camera footage showed motionless bodies lying in Lubyanka station lobby and emergency workers treating victims. 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.
The last confirmed terrorist attack in the Russian capital was in August 2004, when a suicide bomber blew herself up outside a city subway station, killing 10 people.
Responsibility for that blast was claimed by Chechen rebels, and suspicion in today's explosions is likely to focus on them and other separatist groups in the restive North Caucasus region.
Moscow's subway is one of the world's busiest, carrying around seven million passengers on an average workday, and is a key element in running the sprawling, traffic-choked city.
The blasts practically paralysed movement in the city centre as emergency vehicles sped to the stations. Helicopters hovered over the Park Kultury station area, which is near the renowned Gorky Park. Passengers, many of them in tears, streamed out of the station, one man exclaiming over and over "This is how we live!"
At least a dozen ambulances were on the scene.