VOLGOGRAD, Russia - A suicide attacker set off a bomb in the entrance hall of a Russian train station on Sunday, investigators said, killing at least 16 people in the second deadly attack within three days as Russia prepares to host the Winter Olympics.
Authorities said the attacker detonated a shrapnel-filled bomb in front of a metal detector just inside the main entrance of the station in Volgograd, a busy hub north of the violence-plagued North Caucasus region on Russia's southern fringe.
Islamist militants in the North Caucasus have carried out a long string of attacks since President Vladimir Putin came to power in 2000. They now confront him with his biggest security challenge, threatening to disrupt the Olympics that start in the Black Sea resort of Sochi in 40 days.
Footage shown on TV captured the moment of the blast, as a massive orange fireball filled the hall of the stately, colonnaded station and clouds of grey smoke poured out of shattered windows.
The station - a Stalinesque architectural monument with a clocktower and spire topped by a Soviet-style star - was busier than usual, with people travelling home for the New Year, one of the main holidays in Russia.
"People were lying on the ground, screaming and calling for help," a witness, Alexander Koblyakov, told Rossiya-24 TV. "I helped carry out a police officer whose head and face were covered in blood. He couldn't speak."
The city once bore the name Stalingrad in honour of Soviet dictator Josef Stalin, a figure held in opprobrium by many in the North Caucasus.
In the 1940s, Stalin ordered the deportation of tens of thousands of people from the region, including Chechens, to Central Asia on suspicion of harbouring sympathies for Nazi Germany. Many thousands died in exile and transport.
The federal Investigative Committee and other officials initially said a female suicide bomber had blown herself up after a police officer started to approach her near the metal detector because she looked suspicious.
A Russian website with ties to security agencies, Life News, posted a picture of what it said was the suspect's head.