Reports out of the Russian city of St. Petersburg show a city reeling from what are believed to be terrorist attacks. At least one explosion on a subway train has left 10 people dead. This is a developing story, and the details are likely to change as authorities sift through the wreckage.

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There are only two sources of information currently available. The Russian state run media is saying there was one explosion and that there are 10 dead. “According to the very first preliminary information, about 10 people were killed in the explosion,” a source told TASS.

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Accounts on social media are less specific with the number of casualties and suggest that there may have been two coordinated attacks, but do chronicle the chaos above ground as bystanders and rescue workers struggled to get the wounded survivors out of the underground stations.

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There was one bomb, for sure, and rumors of a second may be due to the blast occurring between two subway stations. Authorities are quick to point out that they’re not yet certain about what caused the explosion, yet the early forensic data leaves little doubt.

Russian President Vladimir Putin has made a public statement and expressed his condolences.

Security in St. Petersburg has been strengthened. At least seven of the subway stations have been closed as police investigate.