"We offer our condolences to the families of those killed and all those affected," Kurennoi said, adding that the investigative authorities were already probing into the explosion, but the prosecutors would examine absolutely all aspects of the affair.
"We will do our utmost to clear up the factors that made the terrorist attack possible to rule out such cases in the future," he said, Tass News Agency reported.
St. Petersburg’s prosecutor Sergey Litvinenko is coordinating law enforcers’ activities on site.
Russian president Putin said earlier the investigators are considering various causes, including those linked to terrorism.