Russian authorities say a female suicide bomber from Dagestan detonated a bomb in a passenger bus near the southern city of Volgograd.
A dashcam posted on YouTube shows the bus traveling at a good clip on a three-lane highway, when it's suddenly rocked by a massive explosion that fills the highway with smoke and debris.
RIA Novosti, Russia's official news agency, reports the blast killed at least six people. The organization adds:
"By evening, 28 people had been taken to hospital, including eight in serious condition, a city public health official told RIA Novosti. Around 50 people were believed to be riding the bus at the time of the blast.
"The explosion took place at about 2 p.m. local time (10:00 GMT) in the Kransoarmeisk district in Volgograd, a city formerly known as Stalingrad.
"State-run English language news channel RT quoted a local resident, identified only as Ilya, as saying the road at the scene of the blast was strewn with broken glass.
"'I saw a woman sitting inside the bus. She was covered with blood and I couldn't make out whether she was alive or not. She was just sitting there,' Ilya told RT."
The Christian Science Monitor reports that during the last decade, suicide bombings have become less common in Russia. But tensions between Russia and separatists in Dagestan continue and this bombing is particularly worrisome for Russia because it is hosting the Winter Olympics, soon, and has spent a ton of money trying to secure the country.
The paper adds:
"There was no immediate claim of responsibility for the attack. The ITAR-Tass news agency quoted law enforcement official as saying the woman was married to a man who was member of a militant group in Dagestan.
"President Vladimir Putin has put his personal reputation on the line for Russia to host the upcoming Olympics. He personally lobbied the International Olympic Committee to award Russia the games, and has regularly upbraided government officials for the astronomical sums being spent. By some accounts, the Sochi Olympics will cost upwards of $50 billion, the most expensive on record.
"Sochi was awarded the games with reassurances from Russian officials that the security concerns that have plagued the North Caucasus for decades would not threaten athletes or spectators."