The station, on both the busy Sokolnicheskaya and Tagansko-Krasnopresnenskaya lines, lies beneath the headquarters of the Federal Security Service (FSB).
"I was moving up on the escalator when I heard a loud bang, a blast. A door near the passageway arched, was ripped out and a cloud of dust came down on the escalator," an eyewitness named Alexei told Rossiya 24 TV channel.
"People started running, panicking, falling on each other," he said.
The second blast at Park Kultury, which is six stops away from Lubyanka on the Sokolnicheskaya line, came at 0838 (0438 GMT). It struck at the back of the train as people were getting on board.
"I was in the middle of the train when somewhere in the first or second carriage there was a loud blast. I felt the vibrations reverberate through my body," one passenger told the RIA news agency.
"People were yelling like hell," he said. "There was a lot of smoke and within about two minutes everything was covered in smoke."
The security services said the bomb that went off at Lubyanka station had an equivalent force of up to 4kg of TNT, while the bomb at Park Kultury was equivalent to 1.5-2kg of TNT.
The devices - believed to have been made with the powerful explosive, hexogen, which is more commonly known as RDX - were filled with chipped iron rods and screws for shrapnel.
"The whole city is a mess, people are calling each other, the operators can't cope with such a huge number of calls at a time," said Olga, a BBC News website reader in Moscow. "Those who witnessed the tragedy can't get over the shock."
Vladimir Putin: 'Terrorists will be destroyed'
Moscow's Metro is one of the most-used underground railways in the world, carrying about 5.5 million passengers a day.
The system was partially disrupted following the attacks, but damage to the stations was minimal and both had reportedly reopened by the evening rush hour.
President Medvedev asked officials to increase security on the public transport system nationwide.
"What was being done needs to be substantially strengthened," he said. "Look at this problem on the scale of the state, not only as it applies to a particular type of transport and a particular city."
In a meeting with President Medvedev, FSB chief Alexander Bortnikov said its investigators believed the attacks had been carried out by "terrorist groups related to the North Caucasus".
"This is likely to be our main conclusion, because fragments of the bodies of two female suicide bombers were found earlier at the scene of the incident and examinations show that these individuals came from the North Caucasus region," he said.
Federal prosecutors said they had opened an investigation into "suspected acts of terrorism".
The co-ordinated attacks were the deadliest in Moscow since February 2004, when 40 people were killed by a bomb on a packed metro train as it approached the Paveletskaya station.
MOSCOW METRO ATTACKS
March 2010: Two suicide bombers blow themselves up at Lubyanka station and Park Kultury station, killing 35 people
August 2004: Suicide bomber blows herself up outside Rizhskaya station, killing 10
February 2004: Suicide bombing on Zamoskvoretskaya line, linking main airports, kills 40
August 2000: Bomb in pedestrian tunnel leading to Tverskaya station kills 13
February 2000: Blast injures 20 inside Belorusskaya station
January 1998: Three injured by blast at Tretyakovskaya station
June 1996: Bomb on the Serpukhovskaya line kills four
Six months later, a suicide bomber blew herself up outside another station, killing 10 people. Both attacks were blamed on Chechen rebels.
Federal security forces have scored a series of successes against militants in the North Caucasus in recent weeks.
In February, at least 20 insurgents were killed in an operation by troops in Ingushetia.
Chechen rebel leader Doku Umarov warned in February that "the zone of military operations will be extended to the territory of Russia... the war is coming to their cities".
Last November, he said his Caucasian Mujahadeen had carried out a bombing that killed 26 people on board an express train travelling from Moscow to Russia's second city of St Petersburg.
The attack came six months after President Medvedev declared an end to Russia's "counter-terrorism operations" in Chechnya, in a bid to "further normalise the situation" after 15 years of conflict that claimed more than 100,000 lives and left it in ruins.
Despite this, the mainly Muslim republic continues to be plagued by violence, and over the past two years Islamist militants have stepped up attacks in neighbouring Ingushetia and Dagestan.
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