Two female suicide bombers blew themselves up in separate subway attacks during Monday rush hour in Moscow, killing at least 37 people.
Just before 8 a.m., a bomb rocked Lubyanka station, beneath a federal intelligence office. About 40 minutes later, another blast went off at a station near Gorky Park.
Russian Prime Minister Vladimir Putin blamed Islamic separatists in the Caucasus region, where Russia fought the Chechens a decade ago.
"Terrorists will be destroyed," Putin said.
Security in New York City subways was reportedly beefed up in response to the bombings. There's a "heightened security presence," said MTA spokesman Kevin Ortiz.
Russian television showed video of subway riders lying on the floor, the platform full of smoke.
"People ran for the exits screaming," said Alexander Vakulov, 24.
"It was very scary," said Valentin Popov, 19. "I saw a dead body. Everyone was screaming. There was a stampede at the doors. I saw one woman holding a child and pleading with people to let her through, but it was impossible."
In Washington, President Obama condemned the attacks.
"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," he said in a statement.
The coordinated attacks come six years after Chechen rebels blew up a subway station in Moscow, killing 10 people.