MILAN (Reuters) - Italy's Antitrust authority said on Monday it was looking into how the country's biggest utility Enel had communicated recent material gas and power price increases to its domestic customers.

The authority said that from January it had received complaints from more than 600 customers and small companies about rises in their energy bills triggered by Enel Energia, fully owned by Enel, for the October 2023-January 2024 period.

Customers complained of a lack of clear and written communication from Enel to inform them about the future price increases, something that allegedly deprived them of the chance to opt out from their contracts and switch to another provider.

Enel Energia said in a statement it believed that it had always acted in full compliance with primary and sector regulations, as well as with contractual regulations.

The firm said it was confident that it would be able to demonstrate the full correctness of its actions.

Under new Chief Executive Flavio Cattaneo, state-controlled Enel reported a 12% rise in its 2023 ordinary earnings before interest, taxes, depreciation and amortisation (EBITDA) to 22 billion euros thanks to growth at its retail business in Italy.

(Reporting by Francesca Landini; Editing by Keith Weir)