A second bomb has exploded in the Russian city of Volgograd, killing ten people and raising fears of a wave of terrorist bombings.

It was not immediately clear whether the explosion that ripped through a bus carrying people to work during rush hour this morning was the work of a suicide bomber.

“At ten minutes past eight this morning an explosion occurred on trolleybus 15A in the Dzerzhinsky region of Volgograd. At least 10 people have been killed and 15 injured. The Trolleybus was completely destroyed,” Investigative Committee spokesman Vladimir Markin said in a statement.

On Sunday at least 17 people were killed and more than 40 injured in an apparent suicide bombing on the city’s main railway station.