Bulgaria's interior minister has ordered swift investigation into the blast that blew up the car of a prominent journalist, while making it clear the government is unperturbed by the incident.

"I am absolutely sure that the masterminds of the blast are people who think this is a good tool in the pre-election campaign, which is already underway," Interior Minister Tsvetan Tsvetanov commented on Friday.

He assured that the culprits will be brought to justice and there is no escalation of tensions across the country.

The minister's version of events was backed by the ruling party runner for president Rosen Plevneliev.

"Unfortunately blasts are what we always see during pre-election campaigns," the candidate said.

"Those who target journalists should be held responsible and brought to justice. Bulgaria can move ahead only if it puts in efforts to achieve its goals and cleans up its image."

According to Plevneliev the ruling GERB party leads a positive campaign, unlike its rivals.

An improvised explosive device blew up late on Thursday the car of popular Bulgarian journalist Sasho Dikov, known for his harsh criticism against the center-right government.

No casualties have been reported.

Dikov is program director of private television Kanal 3. Known best for his fiery temper, he told his channel that he "has received absolutely no threats from anyone, no matter how incredible this may sound."

The blast exploded about 10 pm in front of the residential building where Dikov lives and coincided with the visit of European Commission President Jose Manuel Barroso to Bulgaria.

Similar explosions rocked in the middle of July the offices of two Bulgarian opposition parties in Sofia – the conservative Order, Law and Justice Party, RZS and the party of former Prime Minister Ivan Kostov, the die-hard rightist Democrats for Strong Bulgaria.

The blasts came right before the European Commission published its annual report on Bulgaria's progress in the fight against organised crime and corruption and just a day after Bulgaria's centrist and leftist opposition tabled in parliament a no confidence motion against the cabinet of Boyko Borisov, which the two targeted parties supported.

Rumors emerged, suggesting that the blasts were just PR tricks, masterminded by the parties themselves, and drawing parallels to the bomb that exploded in front of the offices of Galeria, an anti-government newspaper, early on February 10 in downtown Sofia.