MOSCOW - A suspected female suicide bomber set off a blast on a bus packed with students in southern Russia on Monday, killing at least five people and raising security fears less than four months before the Winter Olympic Games.
Officials said the explosion that injured nearly 30 people went off at around 2:00 pm (1000 GMT) in the Volga River city of Volgograd, about 900 kilometers (560 miles) southeast of Moscow.
Footage broadcast on state television showed a green and white city bus standing mangled in the middle of the street, its windows blown out on the left side.
"It was an unidentified explosive device," a spokesman for the National Anti-Terror Committee said by telephone.
The Investigative Committee, Russia's equivalent to the US Federal Bureau of Investigations, said officials had opened a formal terror probe.
"A criminal case has been opened under articles outlining terrorism, murder and the illegal use of firearms," the Investigative Committee said in a statement.
An official at the Investigative Committee said police had found the identity papers of a suspected female suicide bomber who they believe was the wife of a rebel commander fighting in Russia's restless North Caucasus.
"She had recently adopted Islam," the unnamed Investigative Committee source told Russian news agencies.
Officials said the packed bus was carrying about 40 passengers at the time of the explosion.
"There were lots of students on the bus," a man named Vladimir, whose daughter survived the explosion, told Moscow Echo radio from Volgograd.
"It was a powerful explosion - a huge blast," he said.
"The bus was torn to pieces. When I came to pick up (my daughter), half the bus was simply not there."