Bulgaria's Prime Minister Boyko Borisov has said his country has to sell state-owned gas grid operator Bulgartransgaz or pay off a fine of up to EUR 300 M, citing EU antitrust regulators.

This comes against the backdrop of an ongoing antitrust investigation launched last year into the Bulgarian Energy Holding's practice of allegedly denying competitors access to the Bulgarian gas transportation network.

Borisov has told the media following a European Council session that the EU Competition Commissioner Margrethe Vestager's words to him that Bulgartransgaz has to be sold are "a heavy political blow" to Bulgaria.

"Otherwise there is an infringement procedure," he is heard saying in an audio file sent to the media by the government's press office.

"They want to impose on us a procedure over the ownership of pipes and compressor stations. We cannot allow that... It is unacceptable to us, whatever the financial sanctions," daily Capital also quotes Borisov as saying.

He has voiced his indignation at the development, pointing to it as an example of where the EU needs reform and adding he asked Vesthager whether the the regulators are scrutinizing all other member states as well.

"We know where the European Union has to be fixed and everybody at the European Council is putting in effort."

Reuters quotes Commission spokesman Ricardo Cardoso as saying that "as is common practice in antitrust investigations, Commissioner Vestager has met with Bulgarian counterparts to discuss the state of play of the investigation."

In October of last year, Borisov said the country was working to make sure "everything" that regards gas control is fully state-owned.