MOSCOW, December 30 (RAPSI) – A criminal case on terrorism and illegal weapons trafficking has been initiated after an explosion destroyed a trolleybus in a Russian southern city of Volgograd on Monday morning, RIA Novosti reported.

The blast on the trolleybus, packed with morning commuters, happened at about 8:10 a.m. (04:10 GMT) killed 10 people and injured 15, according to the authorities.

The blast was most likely caused by an explosive device left in the vehicle’s passenger cabin, Russia’s National Anti-Terrorism Committee said.

Investigative Committee spokesman Vladimir Markin said investigators believe a male suicide bomber was responsible for the attack, which he said was linked to another fatal bombing in Volgograd one day earlier.

Authorities believe an explosion at a railway station on Sunday afternoon that killed 17 people and injured over 40 others was also the work of a suicide bomber.

Markin said that remains of both suspected bombers, which were recovered at the scenes, are undergoing DNA testing.

Investigative Committee official spokesman Vladimir Markin said that the trolleybus explosion was a terrorist attack, making it the second such incident in Volgograd in less than 24 hours.

In another attack in Volgograd in late October, six people were killed and 37 injured when a bomb carried by a young woman from the southern republic of Dagestan detonated while she was travelling on a crowded commuter bus.

The cities blighted by those attacks are located close to the North Caucasus, a multiethnic and volatile region that suffers near-daily attacks on officials, police and civilians by local militant groups.