ST. PETERSBURG, Russia, April 4 (Xinhua) -- The bombing in a subway system in St. Petersburg, Russia, has killed 14 people, up from 11 deaths, Russian Health Minister Veronika Skvortsova said Tuesday.

The blast took place around 14:40 local time (1140 GMT) Monday in a train carriage on the runway between the metro stations Technological Institute and Sennaya Ploshchad (Square) in St. Petersburg, the country's second largest city.

The exact causes and perpetrators behind the attack remain unknown.Russian officials have described the bombing as an act of terror.