The company received payments from the Lithuanian government between 2013 and 2018 for the provision of electricity strategic reserve services, which keep generation capacities outside the electricity market and are used in case of emergency.

"The Commission has reached the preliminary conclusion that the measure constituted State aid," the EU executive said in a statement. "The Commission will now assess the aid to ensure it did not unduly distort competition."

It said it will investigate whether the strategic reserve services were necessary in the period between 2015 and 2018, when Lithuania increased its energy interconnections with neighbouring countries.

Brussels will also assess whether it was appropriate and proportionate for Lithuania to assign the service directly and exclusively to Lietuvos, the statement said.

(Reporting by Francesco Guarascio @fraguarascio)