A second blast in two days has struck the southern Russian city of Volgograd.

According to the vice governor of the region,fifteen people have been killed in an explosion on a trolley bus this morning.

Russian officials put the death toll at eleven.

At least 15 people are believed to have been wounded.

Police and ambulances apparently arrived quickly on the scene as emergency services treated the wounded.

The bus is a shell of its former self; its roof was blown off and debris strewn around the street.

Federal investigators in Russia are calling the attack a “terrorist act.”

Security had already been tightened in Volgograd following Sunday’s suicide bomb attack on the city’s train station.

Investigators have now confirmed at least 17 people died in Sunday’s blast.

The bombings come as the country prepares for the Winter Olympics.

President Putin has put Russia on high alert. However, insurgents have vowed to prevent the 2014 Games in Sochi from going ahead.