Last updated at 1:46 PM Eastern time.
11 people were killed and 39 others were injured in an explosion on a subway car at Sennaya Ploshchad in St. Petersburg, Russia at 2:30 PM local time on Monday, April 3.
Russian security agencies are reporting that they found and disabled another explosive device at another metro station.
Officials have closed all of the St. Petersburg metro stations and the incident is being investigated as a potential terrorist attack. The governor of St. Petersburg has announced that the city will observe three days of mourning.
According to state media, Russian President Vladimir Putin is talking to the Federal Security Service about the situation. Putin was in St. Petersburg for a speaking engagement earlier today, but he is now in Strelna, approximately 20 miles away.
Putin said, "I have already spoken to the head of our special services, they are working to ascertain the cause of the blasts."
"The causes are not clear, it's too early. We will look at all possible causes, terrorism as well as common crime."
Facebook has activated Safety Check, which allows people in the vicinity of the explosion to mark themselves safe. Facebook uses it's Safety Check feature when a large group of people in the same geographic area reference a specific emergency on the social network.
In an interview with CNN, Stanislav Listyev said, "I think that explosion happened in the tunnel between the stations. The smoke was coming out of there. There was nothing on the station itself, everything was fine."
He added, "I didn’t see any injured people. No one was injured on Sennaya square."
The US embassy in Russia tweeted "We are shocked and saddened from the blast in St. Petersburg, as the result of which people died and were injured. We wholeheartedly support the victims and their families."
A port city on the Baltic Sea, St. Petersburg is the second largest city in Russia with a population of 4.9 million people.
Correction: Earlier versions of this story indicated that as few as 9 and as many as 10 people were killed in the explosion. This version has been updated with the latest information we have available.
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Jeff Rooks is a content and social media marketer who masquerades as a craft brewer and can usually be found wearing sneakers and a scarf. When he's not busy pondering beer, food, music, and Star Wars ad nauseam, he's typically traveling the globe with his wife or actively avoiding the yard work. Follow his adventures on Twitter and Instagram.