NEW YORK - The mobile payment wars are heating up.

Wal-Mart Stores Inc., the world's largest retailer, said it is launching its own mobile payment system that will allow shoppers to pay with any major credit or debit card or its own store gift card through its existing smartphone app at the cash register.

It started testing the new payment feature Thursday at its stores in the Bentonville, Ark., area, where the retailer is based. It plans to launch the payment system, called Walmart Pay, in all 4,500-plus U.S. stores early next year.

It's part of Wal-Mart's overall mobile strategy to making shopping easier and faster, but the launch is the latest salvo in the battle for mobile payments that's in the early stages. Wal-Mart has moved into the field as Apple's one-year-old tap-and-pay system is being expanded to other merchants such as Best Buy and KFC and several months after Google launched the Android Pay mobile wallet app and Samsung came out with Samsung Pay. They're all trying to get a piece of what could be a very lucrative business, but none of them has cracked the market so far.

The move signals that Wal-Mart thinks it's best to build its own system to better serve its customers, even as it backs a retail industrywide mobile-payment program that is in the test phase.

"We are creating a seamless shopping experience that includes payment," Neil Ashe, president and CEO of Wal-Mart's global eCommerce, told reporters on a conference call on Wednesday. "It's fast. It's simple, and it's a secure way for customers to use their smartphone."

Twenty-two million customers use the Wal-Mart app each month, and more than half of Wal-Mart's online orders are now coming from a mobile device. This holiday season, Wal-Mart added such new features as allowing online shoppers to check in once they get to the parking lot so they could have their online orders ready for pickup.

Wal-Mart executives said that after evaluating various mobile options, they found that they had different constraints, working only on certain devices or payment types.

Apple Pay requires iPhones. But Google's own tap-and-pay services, Android Pay, and Samsung's Samsung Pay require Android phones.

However, Ashe and Daniel Eckert, Wal-Mart's senior vice president of services, told reporters the system is designed to integrate with other payment applications such as Apple Pay - if the retailer decides to include them.

Wal-Mart's move could be a blow to Merchant Customer Exchange, or MCX, set up a few years ago by a consortium of retailers and restaurants to create an industrywide mobile-payment system. Wal-Mart has been a key player. But Wal-Mart executives told reporters they remain excited about the MCX pilot program for the payment system called "CurrentC."

Wal-Mart's new mobile payment systems works this way: Shoppers download the Wal-Mart app and then select a payment method. At the register, they open up the app and then they activate the camera function to scan a QR code on the reader. That connects the phone to the basket of items they're checking out. Customers can put the phone away, and an e-receipt application will be sent to the app.

Mobile-payment services from Apple, Google, and Samsung all rely on wireless technology called NFC. The customer merely taps the phone next to a payment machine at the store and authorizes the purchase, usually with a fingerprint ID. But it works only in stores with newer, NFC equipment. Samsung goes further in offering a backup: The phone can mimic the old-school magnetic signals produced by card swipes and work with most existing equipment.