Apple’s mobile payments wallet is growing quickly.

The number of Apple Pay transactions in the latest quarter rose 450% from the same period a year ago, CEO Tim Cook said on Tuesday during a conference call with analysts about his company’s quarterly results.

The likely reason: Apple Pay expanded to a number of new international markets in 2016. It is now available in 15 countries including the United States, the United Kingdom, Switzerland, Canada, Australia, China, France, Hong Kong, Singapore, Japan, and Russia.

As usual, Cook didn’t reveal the number of Apple Pay users, revenue from Apple Pay, or the value of those transactions. In the past, Apple has said that one million new users sign up for Apple Pay each week.

Apple Pay debuted in 2014 as a way to let shoppers load their credit card and debit card information onto iPhones’ “mobile wallets.” Customers can then use either their iPhone (or linked Apple Watch) to pay at retail stores equipped with point-of-sale registers supporting near-field communication (NFC) technology, which allows for payments between smartphones and registers. Apple Pay users simply place their phones or watches near the registers’ sensors for payments without having to swipe a card.

Apple Pay competes both in the U.S. and internationally with Google’s rival service Android Pay and Samsung Pay. Apple makes money by charging a small percentage on each transaction.

Cook also revealed on Tuesday that Apple Pay is accepted at 20 million locations worldwide, including 4.5 million in the U.S.

Next, Apple may introduce an extension of its Apple Pay service that would let users send money to one another. The service would challenge PayPal’s popular payments app, Venmo, according to Recode.

This story originally appeared on Fortune.com. Copyright 2017