Two people, including a six-year-old Russian girl, were killed and 10 were taken to hospital in Tiraspol, when two grenades detonated on the vehicle. Two unexploded grenades were discovered later.
"It was not an accident. It was a terrorist attack," Vladimir Antyufeyev said, adding it was designed to destabilize the region sowing panic and discontent with law enforcement agencies.
Antyufeyev thereby dismissed security services' earlier assessment of the attack as one linked to the criminal underworld.
The attack was the second fatal incident to strike public transport in the area in just over a month. On July 6, an explosion blew the roof off a mini-bus taxi in Tiraspol, killing seven and wounding 23.