Bulgaria, which wants to adopt the euro currency, has made genuine progress in bringing its economy closer to those of eurozone countries but has still some work to do, the head of the European Commission said on Friday.

Speaking at a ceremony starting Bulgaria's six-month presidency of the European Union, Jean-Claude Juncker praised Bulgaria's strong public finances and said all countries that meet the criteria should be able to adopt the euro.

"I did not say that Bulgaria will be automatically the next member of the eurozone, but it is heading in the right direction because ... unemployment is falling, the budgetary situation in strong, so when it comes to genuine convergence, Bulgaria has achieved progress," Juncker said.

"It is not quite enough yet and our Bulgarian friends are aware of this, but when it comes to real convergence there has been genuine progress," he said.

Bulgarian officials said on Thursday they wanted to file a formal application in the middle of this year to lock their currency in the Exchange Rate Mechanism 2 (ERM-2) - a two-year stability test for national currencies before joining the euro.

"I am sure that Bulgaria will, or should join the ERM-2 as rapidly as possible," Juncker said.