Bulgaria's Prime Minister Boyko Borisov on Thursday said he had "forbidden" the issue of presidential elections until June.

The vote is due in the autumn. An open race for the office of the President, an office of predominantly ceremonial functions, is not expected to begin before the summer, but some parties are already putting forward candidates.

Borisov told public broadcaster BNT it was "not fair" to raise the issue given the performance of incumbent head of state, Rosen Plevneliev, who is "doing [a great job]" and "has to have the confidence and authority to end his term."

"When it is time for presidential elections, we will talk," Borisov added, casting doubt as to whether Plevneliev will be endorsed for a second term this year.

Pleveniev was elected in 2011 after his name was put forward by Borisov's GERB party.

Prior to becoming head of state he was Regional Development Minister, and GERB's decision to endorse him was seen by many as a way for Borisov to have leverage on the Presidency.

But others have suggested the head of state is pursuing his own agenda on some issues, having adopted a hardline stance against Russsia on Ukraine and on the conflict in Syria.

Plevneliev has also repeatedly declined to voice his plans for the next vote.

GERB's deputy chair Tsvetan Tsvetanov in January said there were five potential candidates that were still being discussed in the party, but a decision was not likely to be announced before the summer.