ST. PETERSBURG, ****** — An ********* Monday afternoon ripped through a subway train in the Russian city of St. Petersburg, ******* at least 10 people and injuring 50 others, the spokesman for the city’s governor told Russian television. The ***** came as Russian President Vladimir ***** was visiting the city, his hometown.

St. Petersburg, ******’s second-largest city with over 5 million residents, is the country’s most popular tourist destination. The two stations that were the site of the ***** are some of the subway’s busiest.

*****, speaking from Constantine Palace in St. Petersburg, said investigators were looking into whether the ********* was a ****** ****** or if there might have been some other cause. He offered his condolences to the families of those ******.

There was no immediate claim of responsibility for the *****.

The unidentified ********* device went off at 2:20 p.m. on a train that was leaving the Technology Institute station and heading to the Sennaya Square station, ******’s National Anti-********* Committee said.

The St. Petersburg subway immediately shut down all of its stations and the national anti-********* body said security measures would be tightened all key transport facilities across ******. Maxim Liksutov, Moscow’s deputy mayor, told Interfax that Moscow authorities were tightening security on the subway in the Russian capital.

Social media users posted photographs and video from the Technology Institute subway station in the city centre, showing ******* people lying on the floor outside a train with a mangled door. Frantic ********* were reaching into doors and windows, trying to see if anyone was there, and shouting “Call an ambulance!”

***** was in St. Petersburg on Monday for talks with Belarusian President Alexander Lukashenko.

“Law enforcement agencies and intelligence services are doing their best to establish the cause and give a full picture of what happened,” ***** said at the start of his talks with Lukashenko.

St. Petersburg governor Georgy Poltavchenko was overseeing the rescue effort.

Russian transport facilities have been the target of previous ****** *******.

Double ******* ******** in the Moscow subway in March 2010 ****** 40 people and ******* more than 100 people. Chechen rebel leader Doku Umarov claimed responsibility for that ****** by two female ******* bombers, warning Russian leaders that “the *** is coming to their cities.”

The high-speed Moscow-to-St.Petersburg train was also bombed on Nov. 27, 2009 in an ****** that left 26 **** and some 100 *******. Umarov’s group also said he ordered this ******.