US President Barack Obama has condemned the suicide bombings in Moscow that killed at least 37 people and injured 65 on packed metro trains.

"The American people stand united with the people of Russia in opposition to violent extremism and heinous terrorist attacks that demonstrate such disregard for human life, and we condemn these outrageous acts," Obama said in a statement.

The two explosions happened on two separate trains on Monday morning.

A Moscow Emergency Ministry spokeswoman said the dead in the first blast included 14 people inside the train and another 11 people on the platform at Lubyanka station in the centre of the city.

The station is underneath the building that houses the main offices of the Federal Security Service, the KGB's main successor agency.

A second explosion hit the Park Kultury station about 45 minutes later. City police spokesman Viktor Biryukov said at least 12 people were killed in that blast.

Gordon Brown said he was "appalled" by the attacks which were carried out by two female suicide bombers.

Mr Brown sent a message of "condolence and support" to President Dmitri Medvedev, added the No 10 spokesman.

The last time Moscow was hit by a confirmed terrorist attack was in August 2004, when a suicide bomber blew herself up outside a city subway station, killing ten people.