Increasingly bitter feud sees mobile chip maker seek import ban on iPhones that allegedly infringe six of its patents.

There was another twist in the increasingly bitter feud between Qualcomm and Apple this week when Qualcomm filed a patent infringement complaint against the iPhone maker.

Qualcomm has petitioned the U.S. International Trade Commission (ITC) to issue a Limited Exclusion Order (LEO) banning the import of Apple products, including iPhones, that allegedly infringe its patents. The mobile chip maker also wants to bar the advertising and sale of infringing products already imported into the country.

Qualcomm said Apple is infringing six patents that enable high performance in a smartphone while extending battery life. The intellectual property (IP) in question is not considered standards essential.

"Qualcomm’s inventions are at the heart of every iPhone and extend well beyond modem technologies or cellular standards," said Don Rosenberg, EVP and general counsel of Qualcomm, in a statement.

"Apple continues to use Qualcomm’s technology while refusing to pay for it," he said.

As well as petitioning the ITC, Qualcomm has also filed a suit with the U.S. District Court for the Southern District of California.

Thursday’s filing is just the latest escalation of an already bitter dispute between Qualcomm and Apple.

Apple hit Qualcomm with a $1 billion lawsuit in January accusing it of numerous anti-competitive practices, including an abusive IP-licensing model designed to extract excessive royalties from suppliers.

Qualcomm filed its own lawsuit in April that claimed Apple had lied to regulators, breached agreements, and knowingly limited the performance of Qualcomm modem chips in the iPhone 7.

In May, Apple began withholding royalty payments to suppliers using Qualcomm technology, which led Qualcomm to cut its fiscal Q3 guidance. It also prompted Qualcomm to sue the aforementioned suppliers.