At least 14 people have been killed and 28 wounded in a suicide bomb attack on a packed trolley-bus in Volgograd, according to a Russian Health Ministry spokesman.

The city was on high alert on Monday following the latest attack, which came a day after a suicide bombing at a train station there killed 17 people.

The blasts have raised safety concerns in the region in the run-up to the 2014 Winter Olympics due to take place in February in Sochi, about 650km southwest of Volgograd.

Al Jazeera's Peter Sharp reports from Volgograd.