passengers wait for the a metro train at Lenin Square metro station in St. Petersburg, Dec. 19, 1996. REUTERS

UPDATED: 9:58 a.m. EDT — Russia's leading prosecutor has reportedly declared the twin explosions in the St. Petersburg subway was an act of terror.

A man left a briefcase in the subway before a fatal explosion in St. Petersburg, Russia, on Monday afternoon, local time, an eyewitness said. "In the span was a blast, the guy left a briefcase, opened the door and went into another car," the St. Petersburg resident told local news outlet RBC. "Only one car."

At least 12 people were killed and at least 50 others were injured, including children.

UPDATED: 9:15 a.m. EDT — The death toll in Monday's deadly explosions in a subway car in St. Petersburg, Russia, has been raised to at least 12 people, according to local news outlet Life. Emergency responders found the dozen lifeless bodies, including eight inside the metro car, two on a subway station platform and another two in a tunnel.

Russian President Vladimir Putin and Belarusian President Alexander Lukashenko, who were meeting in St. Petersburg before the twin blasts were detonated Monday afternoon, were expected to issue a joint live statement afterward.

UPDATED: 8:54 a.m. EDT — More details have begun to emerge following a deadly pair of explosions in a subway car in the Russian city of St. Petersburg on Monday afternoon, local time. At least 10 people were killed and at least 50 others were injured, according to the press secretary for the governor of St. Petersburg, local news outlet NTV reported.

The explosions, which reportedly killed some children, were detonated while the metro car was between the Haymarket Square and Institute of Technology train stations. A suicide bomber has been ruled out in favor of improvised explosive devices being used for the blasts.

Russian President Vladimir Putin, who was in St. Petersburg Monday for a meeting, was reportedly safe and issued a brief statement offering his condolences to the friends and family of those who were killed and injured in the twin explosions.

Keep reading to see images and video from the scene.

UPDATED: 8:45 a.m. EDT — All of the metro stations in St. Petersburg have been closed after two subway explosions there bore "all the signs of a terrorist attack," as Viktor Ozerov, the Defense and Security Committee of the Federation Council, characterized the catastrophe. At least 10 people were killed in the blasts and multiple others were injured, according to reports.

While the official cause of the explosions were not immediately confirmed, Russian President Vladimir Putin — who was scheduled to be in Russia's second-largest city Monday — said it was terrorism.

"The causes of the explosion in the subway in St. Petersburg is not yet known, covers all versions - and domestic and terrorist act", Putin said shortly after the blasts were reported.

Original story:

At least two explosions were detonated in the metro in St. Petersburg on Monday, Russia, BBC News reported. There have been a number of casualties, according to pictures and video footage that have emerged on social media. CNN was reporting there have been "fatalities." At least 10 people may have been killed in the explosions, Russian state-owned news agency Tass reported.

While unconfirmed, social media reports out of Russia have indicated there may have been at least one improvised explosive device. At least 10 people have been injured, according to local news outlet FlashNord Information Agency. Children were among those reported as being injured from the explosion.

Details were scarce, but a live stream from the scene showed emergency responders, including firemen and ambulances, arriving to the scene. There were no immediate reports of what caused the explosion, but local law enforcement likely were not ruling out terrorism as a potential factor. In the immediate term, rescue teams were battling heavy smoke, an emergency official told Sputnik News, a Russian state-owned media outlet.

"Preliminarily, there is strong smoke. Smoke protection service experts have been dispatched. The source of the smoke is being investigated," the unnamed official said. ​"There was an explosion in one of the cars. There are injured and victims."

The blast happened at the "Sennaya ploschad [square]" station.

Terrorism in Europe has been a continental concern in recent years. Monday's explosions came less than two weeks after An Islamic State group-claimed terror attack left at least five people dead following a car and stabbing attack.

Just last week, three people were taken into custody in Russia under suspicion of being involved in a terror cell there, Sputnik news reported on Wednesday.

"As a result of March 28 events held in Moscow Region and Penza Region, the illegal activity of the organized, deeply clandestine structure of the international terrorist organization 'Islamic Party of Liberation' ('Hizb ut-Tahrir Al-Islami') was suppressed," the Federal Security Service said at the time.