killing at least 14 people aboard a trolleybus during today's morning commute and and injured 28.
The explosion comes a day after a suicide bombing in the city killed at least 17 people and injured more than 40.The explosion was apparently set off by a male suicide bomber and remnants of his body have been sent for identification, Russian Investigative Committee said.
The explosions raised concerns about terrorism six weeks before Russia hosts the 2014 Winter Olympic Games in Sochi,which is roughly 620 meters away.
Russian President Vladimir Putin ordered the National Anti-Terrorist Committee to tighten security measures across Russia, with the additional measures in Volgograd.
Investigators say that Monday's blast and the previous day's terrorist attack in a train station are possibly connected.Volgograd has been hit by two terror attacks in December,killing at least 25.
No group has said it was behind either blast.
The Volgograd region has declared a period of mourning until Jan. 3 for the victims of both bombings.