By David Nowak and Sergei Sergeyev
TOLYATTI, Samara Region -- A powerful explosion ripped through a passenger bus Wednesday in the car-manufacturing city of Tolyatti, killing eight and injuring at least 54.
Investigators are treating the blast, which struck during morning rush hour at a busy intersection, as an act of terrorism.
Alexander Bastrykin, head of the Investigative Committee, a semiautonomous body under the auspices of the Prosecutor General's Office, said the blast could have been ordered by militants based in the North Caucasus, Interfax reported.
The "Caucasian trail ... is being investigated, among others," Bastrykin told Interfax.
Investigators are also considering a criminal conflict or accidental detonation as possibilities, said Yury Rozhin, head of the Federal Security Service's Samara region branch.
Read more: The Moscow Times