MOSCOW, March 29 (UPI) -- Explosions set off by female suicide bombers hit two Moscow subway stations during the morning rush hour Monday, killing at least 37 people, officials said.
"It was a terrorist act carried out by ... female suicide bombers," said Moscow Mayor Yury Luzhkov, citing Russia's intelligence agency, the Federal Security Service.
The blasts "were specifically timed to make the most damage," CNN quoted him as saying.
In Washington, the White House issued a statement in which President Barack Obama extended his sympathies and condemned the violence.
"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.
Russia's Emergency Situations Ministry said at least 65 people were injured in the explosions, the first striking the capital's Lubyanka subway station, followed by one at the Park Kultury station on the same train line. The Lubyanka station is near the Kremlin and Russia's FSB, which replaced the former Soviet Union's KGB intelligence force.
CNN reported a Web site associated with Chechen separatists claimed responsibility for the attacks. Russia has been fighting Islamic militants in Chechnya and other areas in the Caucasus.
After the explosions, security was tightened across Russia, Russian information agency RIA Novosti reported.
"It is difficult to prevent such terrorist attacks and to provide security on transport," Russian President Dmitry Medvedev said. "It is necessary to tighten up what we do and to look at the problem on a national scale. Obviously, what we have done before is not enough."
Medvedev pledged Russia "will fight terrorism without hesitation and to the end," The New York Times reported.
Russian Prime Minister Vladimir Putin said he had no doubt the organizers behind Monday's explosions would be punished, RIA Novosti reported.
"It is well known that today a terrible crime against civilians in its effects and disgusting in its character was carried out," Putin said. "I am sure that police will do their best to find and punish the criminals. The terrorists will be destroyed."