By Jesús Aguado

MADRID (Reuters) - Christiana Riley will succeed Tim Wennes as CEO of Santander in the United States, the bank's executive chair, Ana Botin, said on Friday, as Santander undertakes a wider global restructuring.

As part of the changes, Santander will eliminate the three regional divisions in Europe, North America and South America that it launched in 2019 while going forward with the implementation of its five global units, a source familiar with the matter said.

In 2023, Santander, currently the euro zone's biggest lender by market value, rolled out retail, consumer, payments, wealth, and corporate and investment banking units in an attempt to make the bank simpler and boost its value, which remains a work in progress.

Since Botin took over in September 2014, Santander's shares are down around 25%.

"Christiana will become CEO of Santander US and I am confident she is well-placed to lead the next phase of growth in this critical market," Botin said in a message posted on Instagram.

The restructuring takes place at a time when Santander is expanding its footprint in the U.S. in areas such as corporate and investment banking and when it is reviewing its British presence as part of a regular assessment of its major markets, a person familiar with the matter said earlier this month.

Riley joined Santander in 2023 to oversee the lender's business in North America.

Santander, which relies on 10 key markets for the bulk of its business, has one of the biggest auto-lending businesses in the U.S. It wants to use the U.S. to build its own technology platform for consumer banking, including digital-only banking and consumer finance.

It formally launched its U.S. digital bank in October, offering high-yield savings accounts, which could help fund up to $30 billion in loans for vehicle purchases and broaden its retail business in the U.S.

In October Botin said she expected the bank to have a full-service digital bank in the U.S. by the end of 2025 - a crucial step, as Santander's U.S. business has been generating subpar returns.

The changes are part of a wider reshuffle at Santander group. Botin also announced changes for Banco Santander Chile on Instagram, saying that Andres Trautmann, currently head of corporate and investment banking, will take over as country head and CEO, replacing Roman Blanco.

In an internal memo seen by Reuters, Santander said the CEOs of "our core markets will report directly to the group's CEO Hector Grisi."

(Reporting by Jesús Aguado; editing by Emma Pinedo, Jan Harvey and Leslie Adler)