Bulgaria's largest private gas supplier Overgas wrote a letter to the European Commission in December voicing his suspicion that Russia is seeking to "reanimate the South Stream project", Brussels-based website EurActiv claims.

Its report, titled "Bulgarian Gas Wars Uncover Hidden Gazprom Strategies", comes after a spat between the Russian energy giant and Overgas broke out with the former informing the latter of a halt in gas supplies starting January 01, 2016.

Russia's Foreign Ministry later explained the two companies were working to "settle commercial issues", fuelling suspicions that the halt might be caused by overdue payments. Overgas, however, claims it has no prolonged debt to Gazprom and that under its current contract it is to receive gas supplies until at least December 31, 2017.

Overgas CEO Sasho Donchev wrote on December 23, 2015, a week before the developments with Gazprom took place, that he had spoken with the Russian company's deputy head Alexander Medvedev two days earlier and had been informed that supplies would be brought to a halt at the beginning of 2016.

"Any interruption of supplies by Gazprom Export, even for a short period, would lead in all likelihood to the permanent extinction of Overgas as the only remaining competitor in Bulgaria," he is quoted as writing in the letter.

EurActiv, citing recent remarks by Bulgarian Prime Minister Boyko Borisov, suggests Bulgaria "plans to bring russian gas to its borders... Boris prefers to call the project "gas hub" instead of South Stream."

The latter pipeline project was abandoned by Russian President Vladimir Putin in 2014, who then said it could not be carried out due to opposition from Brussels.

Days later Borisov suggested Bulgaria should set up a gas hub at its borders, a project which reportedly has support from the EU Commission and which was officially called "Balkan" late last year.

The developments also come against the backdrop of Gazprom's plans to withdraw from Overgas, with DOnchev also saying the two companies "are in a stage of separation" and calling the divorce with Gazprom "a question of efficiency".