Russian Metro Bomb Blast Kills at Least 10

At least 10 people were killed in a blast on the St. Petersburg metro Monday, three state-run Russian news agencies said. Authorities say the explosion is a terrorist attack, reports CNN .

An explosion tore through a train as it was traveling between two stations in Russia's second-biggest city, injuring dozens more.

A second device was found and defused at another station, Russia's Anti-Terrorism Committee said. No group has claimed responsibility for the attack, which led to the shutdown of the city's metro system.

President Vladimir Putin, who had been in St. Petersburg earlier in the day, said all causes were being investigated, including terrorism. Russian Prime Minister Dmitry Medvedev described the explosion as a "terrorist act."