Apple Inc's most important new phone for years will be called the iPhone X, according to a leak of the company's latest mobile operating system.

Strings of software code inside of the leaked operating system, first detailed by Apple news website 9to5Mac, show the expected three new phones will be called the iPhone 8, iPhone 8 Plus, and iPhone X. App and game developer Steven Troughton-Smith discovered the names in the software and tweeted about it on Saturday.

New iPhones are due out on Tuesday. Credit:AP

The iPhone 8 and iPhone 8 Plus are successors to the current iPhone models, while the iPhone X is the premium version with an all-new design, crisper OLED screen, improved cameras, and a 3-D facial recognition scanner for unlocking the device.

The "X" in the iPhone's name may be a reference to this model being a special 10th anniversary edition. The iPhone 8 and iPhone 8 Plus will look similar to the iPhone 7 and iPhone 7 Plus, but include faster processors, Bloomberg News has reported. The new devices will be unveiled at an event on Tuesday. An Apple spokeswoman declined to comment.