Apple has apologised for slowing down older iPhones after customers accused the firm of trying to force them into buying newer models.

Apple admitted it had "downclocked" older models' central processing units (CPU) but said it did so to reduce the strain on dated batteries and stop the devices from unexpectedly shutting down.

It came after years of speculation from Apple customers that their older handsets were being slowed down in a bid to entice them into an upgrade.

Amid a wave of class action lawsuits over the "deceptive, immoral, and unethical" phone slowing, Apple has issued an apology and vowed to be more transparent with customers over the capacity of iPhone batteries.

In a post on its website, the tech giant said: "We know that some of you feel Apple has let you down. We apologise.

"There's been a lot of misunderstanding about this issue, so we would like to clarify and let you know about some changes we're making.

"First and foremost, we have never - and would never - do anything to intentionally shorten the life of any Apple product, or degrade the user experience to drive customer upgrades.

"Our goal has always been to create products that our customers love, and making iPhones last as long as possible is an important part of that."

Apple said the slowdown experienced by owners of older phones was exacerbated by the "chemical ageing of the batteries".

It also announced that it would cut the price of a battery replacement for anyone with an iPhone 6 or later - and not covered by the Apple Care maintenance plan - from $79 to $29, starting in January and ending in December next year.

Apple has not yet confirmed the size of the discount for European customers, with battery replacements for those not covered by Apple Care or the standard warranty currently priced at €89.

An update to the iPhone operating system will also be released in early 2018, which Apple said would give users a better understanding of the health of their iPhone battery.