Female suicide bombers detonated explosions that rocked two subway stations in central Moscow during rush hour on Monday morning, killing at least 35 people, officials said, CNN reported.
"It was a terrorist act carried out by the female suicide bombers," said Moscow Mayor Yury Luzhkov, citing Russia's intelligence agency, the Federal Security Service. "They were specifically timed -- for ... the train was nearing the station -- to make the most damage.
"The blast was caused by 300 to 400 grams of explosives," he said.
Forensic teams were combing wreckage from the underground blast for clues.
The blasts killed at least 35 people and wounded 40 others, Russia's Emergency Situations Ministry said. The casualty tolls were fluctuating immediately after the blasts.
The first explosion occurred about 8 a.m. at Lubyanka subway station, killing at least 23 people and injuring 20.
The Lubyanka station is near the Kremlin and the nation's intelligence service, the Federal Security Service.
Another blast happened about 30 minutes later at Park Kultury station, on the same train line. The Emergency Situations Ministry reported 12 dead in the second explosion, with 20 more injured.
Yulia Shapovalova with Russia Today TV was at the second station at the time of the blast.
"The staff members started urgently evacuating people, so that meant they probably knew about the first blast at the Lubyanka station," she said. "All the people -- a huge crowd of people -- slowly started to move. ... As soon as I got upstairs, I heard the blast."
Millions of commuters use the Moscow metro system every day.
A Web site associated with Chechen separatists claimed responsibility for the attacks.
Immediately after the explosions, officials had cast suspicion on the separatists.
Chechens have long fought for independence from Russia.
Chechnya is a southwestern Russian republic, in the Caucasus Mountains region. Chechnya's population of 600,000 to 800,000 is primarily made up of Sunni Muslims and Russian Orthodox Christians. Thousands have been killed and 500,000 Chechen people have been displaced in their conflict with Moscow.
A Chechen female suicide bomber in August 2004 killed nine people and herself, and wounded 51 others, when she detonated a bomb outside a subway station in northeastern Moscow. In February 2004, a suicide bomber detonated a bomb on a Moscow metro train, killing 40 people and injuring 100 others. A suicide attack in 2003 killed 15 people at a Moscow concert.
Chechen terrorists killed hundreds in 2004 at a school in Beslan, Russia. They also were suspected in the downing of two Russian airplanes that year in an attack that killed 89.