A female suicide bomber blew herself up in the entrance hall of a Russian train station on Sunday, killing at least 13 people in the second deadly attack in the space of three days as the country prepares to host the Winter Olympics.
The state Investigative Committee said the bomber detonated her explosives in front of a metal detector just inside the main entrance of Volgograd station. Footage shown on TV showed a massive orange fireball filling the hall and smoke billowing out through shattered windows.
Volgograd is a city of around 1 million people, about 430 miles (690 km) northeast of Sochi, where the Winter Olympics - a major prestige project for President Vladimir Putin - will open on February 7. It lies close to Russia's North Caucasus, a strip of mostly Muslim provinces plagued by near-daily violence in a long-running Islamist insurgency.
Insurgent leader Doku Umarov, a Chechen warlord, urged militants in a video posted online in July to use "maximum force" to prevent Putin staging the Olympics. An attack by a female suicide bomber killed seven people in Volgograd on October 21.
On Friday, a car bomb killed three people in the southern Russian city of Pyatigorsk, 270 km (170 miles) east of Sochi. A spokesman for Russian investigators said in a statement that at least 13 people died in Sunday's blast while a health ministry spokesman told Rossiya-24 television that as many as 50 people were wounded. The station was busier than usual, with people travelling home for the New Year holidays.
TV footage showed emergency services carrying out victims, with at least one body lying motionless on the ground. "I heard the blast and ran toward it," a witness, Vladimir, told Rossiya-24.
"I saw melted, twisted bits of metal, broken glass and bodies lying on the street." Sunday's attack was the deadliest to strike Russia's heartland since January 2011, when Islamist insurgents killed 37 people at a Moscow airport.
(Reporting by Alissa de Carbonnel; Editing by Mark Trevelyan)