Apple has expanded its legal battle against Qualcomm, accusing the US chip maker of charging for invalid patents in the latest twist in the clash between the two tech giants.

In legal filings in a federal court in California on Tuesday, Apple claimed that several Qualcomm patents were invalid because they conflict with existing patents, while other patents were not essential for cell phone communications, according to details of the lawsuit reported by The Wall Street Journal.

In January the iPhone maker filed a lawsuit complaining that Qualcomm -- which produces chips widely used in smartphones and tablets around the world --abused its market power to demand unfair royalties, and demanded billions of dollars in compensation.

Apple filed two similar complaints against Qualcomm in China days later.

However Qualcomm countersued in April, claiming that Apple breached agreements and encouraged regulatory attacks worldwide on Qualcomm.

"Qualcomm's illegal business practices are harming Apple and the entire industry," Apple said in an email Tuesday to AFP.

"They supply us with a single connectivity component, but for years have been demanding a percentage of the total cost of our products - effectively taxing Apple's innovation."

Qualcomm, in a statement by legal counsel Don Rosenberg, denied the accusations.

Apple "knows well" that "Qualcomm's innovations are at the heart of every iPhone and enable the most important uses and features of those devices," Rosenberg said.

"It simply is untrue that Qualcomm is seeking to collect royalties for Apple innovations that have nothing to do with Qualcomm's technology."

In January, the US Federal Trade Commission hit Qualcomm with an antitrust suit alleging it abused its dominant market position for processors, resulting in higher prices for consumers.

The complaint said Qualcomm's practices amount to "unlawful maintenance of a monopoly in baseband processors," which are devices that enable cellular communications in phones and other products. Qualcomm rejected the claims as "flawed".

The San Diego, California, group in 2015 agreed to pay $975 million to settle antitrust charges in China.

Qualcomm is challenging a European Union competition inquiry which could result in a fine of up to 10 percent of its annual sales, which amounted to $26.5 billion in 2015.

Source: AFP