At least 37 people have been killed after two female suicide bombers blew themselves up on Moscow Metro trains in the morning rush hour, officials say.
The first blast occurred in the central Lubyanka station at 0756 (0356 GMT). Police said the dead included 14 people inside a train and 11 on the platform.
The second explosion came about 40 minutes later at the Park Kultury station, where 12 people were killed.
No-one has said they carried out the worst attack in the capital since 2004.
But the BBC's Richard Galpin in the Russian capital says past suicide bombings there have been blamed on Islamist rebels fighting for independence in the troubled North Caucasus region of Chechnya.
Moscow's metro is one of the busiest subways in the world, carrying some 5.5m passengers a day.
'No fire'
Emergency services ministry spokeswoman Irina Andrianova said the first explosion tore through the second carriage of a train as it stood at Lubyanka.
CCTV footage posted on the internet showed motionless bodies in the lobby and emergency workers treating victims.
The station, on both the busy Sokolnicheskaya and Tagansko-Krasnopresnenskaya lines, is close to the headquarters of the Russian Federal Security Service (FSB).
The second blast at Park Kultury, which is also on the Sokolnicheskaya line, came at 0838 (0438 GMT). It struck at the back of the train as people were getting on board.
Helicopters hovered over the Park Kultury station area, which is near the renowned Gorky Park.
"Two female terrorist suicide bombers carried out these bombings," Moscow Mayor Yuri Luzhkov told reporters gathered outside Park Kultury.
Federal prosecutors said they had opened an investigation.
Prime Minister Vladimir Putin, who is currently visiting Siberia, is "receiving detailed information from security agencies and social services about the work on helping the victims", a spokesman said.
Russian forces have scored a series of successes against militants in recent weeks. In February, at least 20 insurgents were reportedly killed in an operation by Russian security forces in Ingushetia.
There was a major attack on the Moscow Metro in February 2004, when at least 39 people were killed by a bomb on a packed train as it approached the Paveletskaya Metro station.
Six months later, a suicide bomber blew herself up outside a station, killing 10 people. Both attacks were blamed on Chechen rebels.
In November, the Caucasian Mujahadeen claimed responsibility for a bomb that killed 26 people on board an express train travelling from Moscow to Russia's second city of St Petersburg.