MOSCOW - An explosion on a bus in the southern Russian city of Volgograd killed four people and injured seven others on Monday, the Interfax news agency reported, citing regional emergency officials.
An Emergency Situations Ministry official in Moscow confirmed an explosion occurred but had no details.
The cause of the blast was not immediately known but it may raise fears it could have been an attack by Islamist militants in the North Caucasus, a string of provinces to the south of Volgograd.
