Story highlights Russian news agency says remains of bomber to be examined

Russia authorities say preliminary information points to a female suicide bomber

Video appears to show explosion inside the main doors to the station

Bomber reportedly was approaching metal detector when attack occurred

A massive explosion at a train station in the Russian city of Volgograd killed at least 16 people, including one police officer, the Investigative Committee of Russia said on its website Sunday.

The head of the committee, Vladimir Markin, said 16 people had been killed and 34 people were injured, including a 9-year-old girl.

The suspected female suicide bomber set off the device before she could pass through a metal detector, Markin said, citing available information at the time.

Later, Markin told Russian news agency Ria Novosti the remains of the bomber will undergo DNA testing.

He said the bomber used the equivalent of 10 kilograms of TNT and included shrapnel.

Investigators also found an unexploded grenade.

Video taken from an outside security camera shows a huge fireball inside what appears to be the main entrance of the three-story stone building followed by a steady trail of smoke coming out shattered windows.

Photos: Deadly blasts in Russian city Photos: Deadly blasts in Russian city Deadly blasts in Russian city – A bomb blast tore through a trolleybus in Volgograd, Russia, on Monday, December 30, a day after a suicide bombing at the city's main railway station. Hide Caption 1 of 10 Photos: Deadly blasts in Russian city Deadly blasts in Russian city – An ambulance leaves the site of a trolleybus explosion. Hide Caption 2 of 10 Photos: Deadly blasts in Russian city Deadly blasts in Russian city – Experts, firefighters and police officers examine the scene of the blast. Hide Caption 3 of 10 Photos: Deadly blasts in Russian city Deadly blasts in Russian city – Police officers examine the area around the site of the explosion. Hide Caption 4 of 10 Photos: Deadly blasts in Russian city Deadly blasts in Russian city – A demolition expert walks among the wreckage. Hide Caption 5 of 10 Photos: Deadly blasts in Russian city Russian train station rocked by blast – Russian security forces stand guard outside a train station in Volgograd, following a suicide bomb attack on Sunday, December 29. Hide Caption 6 of 10 Photos: Deadly blasts in Russian city Russian train station rocked by blast – A police officer guards the main entrance to the station. Hide Caption 7 of 10 Photos: Deadly blasts in Russian city Russian train station rocked by blast – Bodies lie covered on the ground as police continue to investigate the scene. Hide Caption 8 of 10 Photos: Deadly blasts in Russian city Russian train station rocked by blast – Police investigators inspect debris at the scene of the explosion. Hide Caption 9 of 10 Photos: Deadly blasts in Russian city Russian train station rocked by blast – An officer stands guard outside the station. Hide Caption 10 of 10

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The bombing occurred at about 12:45 p.m. local time (3:45 a.m. ET), officials said.

President Vladimir Putin posted a message on the Kremlin's website sending his condolences to the family of those killed and wishing a quick recovery to those hurt.

Prime Minister Dmitry Medvedev ordered the emergency and health ministries to provide "all necessary assistance" to the wounded.

Ria Novosti reported that the regional governor said at least half of the wounded are in critical condition.

It is the second bombing in the southern Russian city in two months and comes less than six weeks ahead of the Winter Olympics in Sochi, located less than 1,000 kilometers (620 miles) from Volgograd.

No one has claimed responsibility for the attack.

JUST WATCHED See moment of train station blast Replay More Videos ... MUST WATCH See moment of train station blast 00:44

"There can be no justification for such barbarous attacks." said NATO Secretary General Anders Fogh Rasmussen. "NATO and Russia stand together in the fight against terrorism., including by working together on technology to prevent attacks on public transport systems."

A White House spokeswoman said, "Our hearts go out to the victims and their families."

In October, a bomber blew up a passenger bus , killing six people and wounding more than 30 others. Russian media reported that a female Islamist suicide bomber from the Russian region of Dagestan was responsible for the attack.

Volgograd, once called Stalingrad, is a major rail hub in the region, and each day thousands of passengers pass through the station, many on their way to Moscow. The station likely was packed with holiday travelers.

The restive region of Chechnya is also located in this southern portion of Russia.