MEXICO CITY, Oct 18 (Reuters) - Mexican financial startup Stori on Wednesday began offering a savings account with the unusually high yield of 15%, a senior executive told Reuters, in a sign of growing competition among digital banking firms seeking to lure Mexicans who lack bank accounts.

Data from Mexico's financial products watchdog Condusef shows that the accounts would be the highest-yielding ones offered in the local financial sector.

Other Latin American fintechs like Brazil's Nubank and Argentina's UALA have also launched savings accounts this year in Mexico, where data from the national statistics agency showed less than half of the population has savings accounts.

Stori, which last year reached a valuation of at least $1 billion, giving it so-called unicorn status, has offered credit cards for the unbanked with credit limits starting at 500 pesos ($28), in a country where only about a third of adults has any kind of consumer loan, according to official data.

Stori's new offering aims to reach individuals outside the traditional banking system, "making a product typically for rich people, popular and democratic," said Marlene Garayzar, the company's co-founder.

Those wishing to open the accounts need to sign up to a waiting list that opens on Wednesday, with the first accounts to be opened at the end of October.

The Bank of Mexico has set it benchmark interest rate at 11.25%. The Mexican arms of Nubank and UALA both offer 9% yields on their savings accounts, already much higher than most banks.

The announcement follows Stori's acquisition of financial firm MasCaja, which provided it a new license to broaden its product portfolio.

Nubank's Mexico unit has attracted more than a million customers since it launched accounts in May, according to company data.

Stori expects to reach 3 million savings account holders by the end of next year, said its General Manager of New Products Sergio Duenas.

($1 = 18.0044 Mexican pesos) (Reporting by Valentine Hilaire; Editing by David Alire Garcia, Christian Plumb and Marguerita Choy)