After launching in the U.K. earlier this year, Apple is set to expand its mobile payments service, Apple Pay, to several new international markets this year and next.

In addition to reporting earnings on Tuesday, Apple CEO Tim Cook announced a partnership with American Express to bring the mobile payments service to Australia and Canada this year, and to Spain, Singapore and Hong Kong in 2016.

Introduced in 2014, Apple Pay AAPL lets users upload credit and debit card information to a “mobile wallet.” Customers can then use their iPhone or Apple Watch to pay at retail stores in the U.S. and U.K. that have point-of-sale registers equipped with near field communication technology, known as NFC.

People can also use their Apple Pay accounts to pay for items within apps if the app developer has integrated the service. Target TGT , Airbnb, Uber, and Amazon AMZN are among the companies that have done so.

Apple’s partnership with American Express AXP will put Apple Pay in new territory at a time of stiff competition from Google’s rival, Android Pay. Android Pay, introduced a month and a half ago, is unavailable overseas.

Although Apple has a head start on its international expansion, it still lacks two other major credit card providers, Visa and MasterCard. Furthermore, American Express is the smallest of the Big Three credit card providers.

Apple made no mention of how many overseas merchants it expects to accept Apple Pay using American Express. Indeed, Apple has released scant data even in markets where the service has been available for some time.

But on Monday, research firm Phoenix Marketing International published a report that indicated the service may not be growing as fast as expected. According to the report, only 14% of U.S. households with credit cards had signed up for Apple Pay by the end of September.

But in the analyst call Tuesday, Cook reassured investors by saying that the number of transactions using Apple Pay is growing in the double digits on a monthly basis.

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