MOSCOW - At least 14 people were killed Monday when a suicide bomber blew himself up on a packed trolleybus in Volgograd, raising new concerns about security at the Sochi Olympics a day after a deadly attack on the southern Russian city's train station.
President Vladimir Putin ordered stepped-up security across the country after the trolleybus bombing at the peak of the morning rush and Sunday's suicide attack blamed on a suspected female suicide bomber which claimed 17 lives.
The attacks on Volgograd, which until this year had no record of recent unrest, raised alarm about whether the ongoing anti-Kremlin insurgency in the Northern Caucasus could affect the Sochi Winter Games which open on February 7.
The force of Monday's blast destroyed the number 15A trolleybus, which was packed with early morning commuters and was turned into a tangle of wreckage with only its roof and front remaining.
Health ministry spokesman Oleg Salagai told Russian state television that 14 people were killed and 28 wounded.
Russian investigators have opened a criminal probe into a suspected act of terror as well as the illegal carrying of weapons, the Investigative Committee said.
"The explosives were detonated by a male suicide bomber, fragments of whose body have been found and taken for genetic analysis to establish his identity," said spokesman Vladimir Markin.
He said four kilogrammes (nine pounds) of TNT equivalent had been used and noted that the explosives were identical to those used in Sunday's train station bombing.
"This confirms the theory that the two attacks are linked. It is possible that they were prepared in the same place," he added.