Citigroup's global head of retail banking and mortgages, Jonathan Larsen, who has been known as an advocate of digital banking, resigned for personal reasons, the lender said.

The New York-based bank is yet to choose a replacement for his "critical role," it said in an internal memo dated Dec. 9. Citigroup spokesman James Griffiths confirmed the contents of the document.

In interviews with Bloomberg in 2014 and 2015, Larsen, who was based in Hong Kong, highlighted the firm's ambitions for doubling digital-banking users in Asia over five years and for boosting its wealth assets under management in the region.

He said that digital banking would help the lender to boost client accounts and revenue, meeting demand from Asia's burgeoning middle class without the costs of extra brick-and-mortar branches.

Larsen joined Citigroup in 1998. Named global head of retail banking in 2012, he added oversight of U.S. consumer banking and mortgages to his role in June last year. Larsen couldn't be contacted through his office number. His exit was reported earlier by The Asset magazine.

Griffiths said Larsen was leaving for personal reasons.

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