"There is no way for us to integrate terrorists, it is not fair," Bulgarian Prime Minister has said.

Borisov has told reporters following the attacks in Brussels on Tuesday that Europe is taking "measures after measures [to make sure these people] are well off," apparently referring to migrants coming into Europe from the Middle East.

He has also called the development "an absolute failure" of the foreign policy of a number of states, adding "everyone was angry at [Merkel] for being so humane to those people."

"There is nowhere in this world they are so integrated, there is nowhere in this world where they are being taken so much care of," Borisov has added.

"And then, to hit us in the hear of Europe this way is not fair."

It is not yet clear who is behind the blasts, but authorities describe them as a "terror attack".

Earlier, Borisov was quick to issue a statement of condemnation, saying Sofia wanted to show "solidarity" with Brussels.

"Brussels is not simply the Bulgarian capital. It is the capital of united Europe... Today, more than ever, all Europeans must show the entire world that we will not allow terrorism to destroy our civilization. I know we will do it in the most convincing way possible, because it is part of our common values, of our common morality and culture."

"I extend the deepest condolences to the families of victims and wish a speedy recovery to those wounded."