The European Commission said on Wednesday the investigation would allow interested third parties to comment on the measures.

The Estonian government lent 8.3 million euros to the airline in December last year to allow it to continue operating flights before its planned restructuring in early 2013.

Estonia had provided a total 57.2 million euros in capital to the carrier between 2009 and 2012.

The EU executive said these measures may have given Estonian Air an unfair advantage.

"At this stage, the Commission has doubts that these four previous measures were carried out on terms that a private player operating under market conditions would have accepted. If they were not, they would involve state aid in the meaning of EU rules," it said.