Apple is cooperating with US government inquiries into its secret slowdown of older iPhones, disrupting its efforts to move past an issue that irked customers whose devices were bogged down.

The company acknowledged the inquiries late Tuesday (30 January) after both The Wall Street Journal and Bloomberg reported the US Justice Department and Securities and Exchange Commission were investigating how investors had been affected by Apple's handling of the incident.

A software update released in 2016 began to slow down older iPhones when their batteries weakened to prevent them from abruptly switching off. But Apple did not fully disclose what it was doing until December 2017.

The tech giants has since apologised for not being more candid and is replacing batteries on iPhone 6 models and earlier models for £20 ($29), a £35 ($50) discount.

The Cupertino, California, company is also working on another software update that will give consumers the option of turning off the slowdown feature, if they are willing to risk a sudden shutdown. That free update, due out this spring, will also include a gauge for measuring the battery's strength.

In its latest statement, Apple reiterated its belief that it had been acting in the best interest of its customers by extending the lives of their iPhones. Many consumers, however, remain convinced that the company torpedoed the older iPhones to prod them to upgrade to the latest — and more expensive — iterations released last fall.

"We have never — and would never — do anything to intentionally to shorten the life of any Apple product, or degrade the user experience to drive customer upgrades," Apple stated. "Our goal has always been to create products that our customers love." Despite its contrition, Apple is still grappling with the fallout.

Authorities in France are in the middle of an investigation to ascertain if Apple violated laws protecting consumers in that country and lawyers in the US are pursuing a variety of class-action lawsuits on behalf of millions of consumers. Meanwhile, the head of the commerce committee in the US Senate had previously sent a letter to Apple demanding more information about the iPhone slowdown.

Apple had been due to respond by 23 January but was granted an extension and is now expected to offer an explanation by the end of this week, said Frederick Hill, a spokesman for senator John Thune, a South Dakota Republican who confronted the company. Both the Justice Department and the SEC have declined to comment on their investigations, offering no clues about what piqued their interest.

Apple's delayed disclosure of the iPhone slowdown does not appear to have done significant harm to investors so far. Just a few weeks after Apple disclosed it had been slowing down older iPhones, the company's stock surged to an all-time high, despite consumer outrage.

The shares have since retreated, but that downturn has been driven by concerns about lacklustre demand for its expensive iPhone X.