Interfax news agency quoted an unnamed source as saying the blast, which occurred when the train was between two stations, was caused by a bomb filled with shrapnel.

The train was apparently arriving at the Technology Institute station from Sennaya (Ploshchad) station. (Euronews)

BREAKING: Blast hits #SaintPetersburg metro https://t.co/8Z0ONCDCRI pic.twitter.com/hEsiPCeXyg

— RT (@RT_com) 3 aprile 2017