MOSCOW -- Two female homicide bombers blew themselves up on Moscow's subway system as it was jam-packed with rush-hour passengers Monday, killing at least 38 people and wounding 102, officials said.
The head of Russia's main security agency said preliminary investigation places the blame on rebels from the restive Caucasus region that includes Chechnya, where separatists have fought Russian forces since the mid-1990s.
The first explosion took place just before 8 a.m. at the Lubyanka station in central Moscow. The station is underneath the building that houses the main offices of the Federal Security Service, or FSB, the KGB's main successor agency.
SLIDESHOW: Moscow Subway Bombing (Warning: Graphic Content)
A second explosion hit the Park Kultury station about 45 minutes later.
"I heard a bang, turned my head and smoke was everywhere. People ran for the exits screaming," said 24-year-old Alexander Vakulov, who said he was on a train on the platform opposite the targeted train at Park Kultury.
"I saw a dead person for the first time in my life," said 19-year-old Valentin Popov, who had just arrived at the station from the opposite direction.
In a televised meeting with President Dmitry Medvedev, Federal Security Service head Alexander Bortnikov said body fragments of the two bombers pointed to a Caucasus connection. He did not elaborate.
"We will continue the fight against terrorism unswervingly and to the end," Medvedev said. Prime Minister Vladimir Putin, on an official trip to Siberia, was being kept informed of developments, news reports said.
The blasts practically paralyzed movement in the city center as emergency vehicles sped to the stations.
In the Park Kultury blast, the bomber was wearing a belt packed with plastic explosive and set it off as the train's doors opened, said Vladimir Markin, a spokesman for Russia's top investigative body. The woman has not been identified, he told reporters.
A woman who sells newspapers outside the Lubyanka station, Ludmila Famokatova, said there appeared to be no panic, but that many of the people who streamed out were distraught.
"One man was weeping, crossing himself, saying 'thank God I survived'," she said.
The last confirmed terrorist attack in Moscow was in August 2004, when a homicide bomber blew herself up outside a city subway station, killing 10 people. Responsibility for that blast was claimed by Chechen rebels.
Russian police have killed several Islamic militant leaders in the North Caucasus recently, including one last week in the Kabardino-Balkariya region. The killing of Anzor Astemirov was mourned by contributors to two al-Qaida-affiliated Web sites.
The killings have raised fears of retaliatory strikes by the militants.
In February, Chechen rebel leader Doku Umarov warned in an interview on a rebel-affiliated Website that "the zone of military operations will be extended to the territory of Russia ... the war is coming to their cities."
Umarov also claimed his fighters were responsible for the November bombing of the Nevsky Express passenger train that killed 26 people en route from Moscow to St. Petersburg.
The Moscow subway system is one of the world's busiest, carrying around 7 million passengers on an average workday, and is a key element in running the sprawling and traffic-choked city.
Helicopters hovered over the Park Kultury station area, which is near the renowned Gorky Park.
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