British challenger bank Monzo today announced the initial roll-out of its financial app and connected Mastercard debit card in the U.S. market. Monzo does not currently have a U.S. banking charter, but it initially will operate with a yet-to-be-announced partner bank.

Tom Blomfield, CEO and co-founder of Monzo, told Bank Innovation that his company’s work with U.S. regulators on a full banking license is ongoing, and that means it needs a U.S. CEO. “One of the primary requirements is the naming of a U.S. CEO, and we actively are working to establish the right person for that role,” he said in an email. The bank already has started to build a team based in Los Angeles.

The mobile-first bank has racked up more than 2 million users in the U.K. in just four years and currently is adding about 200,000 users per month. Blomfield said the company is aiming to build similar momentum in the U.S. by building off a “grassroots” movement, starting with an in-person sign-up campaign along with live events.

Monzo will work with its U.S. customers to build out the particular features they’re seeking, Blomfield said. The company said the first version of the app will include instant spending notifications, peer-to-peer payments, savings envelopes called “pots,” phone support and fee-free foreign transactions. “Monzo will develop the U.S. version into a fully-featured digital account that can be accessed from a smartphone and will have the ability to extend into new Monzo and third-party financial services,” Blomfield said.

Whether Monzo’s customer service-centric strategy in the U.K. will translate to the U.S. market is yet to be seen. “There is an opportunity to educate the market about what a digital bank can do for its users, whether that is through the tap-to-pay feature on debit and credit cards we see becoming more widespread or the ease-of-use in managing all their money from one single interface,” Blomfield said.

Stephen Bird, CEO of Citi Global Consumer Banking, at a New York City event this week, said challenger banks, in general, have a hard road in the U.S. market. The U.S. is “still very fragmented” in comparison with markets like the U.K., which has a very different regulatory environment, he noted.

Monzo was founded in the U.K. in 2015 and has a valuation north of $1 billion.