Moscow ? A strong bomb shredded a passenger bus Wednesday, killing eight people and injuring more than 60 in a central Russian city known for gang violence.

One official speculated the blast in Togliatti was a terrorist attack, but others said that was only one possibility. They said investigators were also looking into whether it resulted from a turf battle between criminals or even the careless handling of explosives.

Police in the Volga River city also weren’t immediately sure whether the bomb was hidden inside or beneath the bus or carried on, officials said.