VILNIUS (Reuters) - The Lithuanian arm of British insurer Aviva will return 349,000 euros (£) to customers after the Baltic country's central bank ruled it had not acted in their best interests.

Aviva Lietuva, indirectly owned by Aviva Group Holdings Ltd, said on Thursday it would return the money to about 50,000 life insurance customers, equating to an average of just under 7 euros each, although it did not admit any wrongdoing.

The central bank said Aviva Lietuva had breached investment law in its handling of customers' money in 2016 and 2017.

It said the company invested clients' money into retail funds, instead of identical funds for institutional clients that charge lower fees but don't pay rebates on the fees. It then pocketed the rebates, instead of sharing them with customers.

"We will not tolerate such actions ... when a company chooses its investments for the benefit of the company and not its clients," said the central bank, which oversees Lithuanian insurance and investment markets.

A spokeswoman for Aviva Lietuva said the company believed it had acted in best interests of its clients.

"Our fee structure was formed according to market practice," she said in a statement. "For most of our clients, the fee structure was financially neutral or even beneficial".

(Reporting by Andrius Sytas; Editing by Mark Potter)