Apple's latest move in the legal battle with Qualcomm is the inquiry to the U.S. Patent and Trademark Office to declare the chipmaker's patents invalid.

The iPhone maker on Thursday filed petitions with the US Patent and Trademark Office, asking for the four Qualcomm patents be canceled, Bloomberg reports. Those patents are at issue in a fight between the companies over licensing fees that Qualcomm receives for its mobile technology.

Apple claims that a total of four patents -- related to how to focus a digital camera, a device that works as a phone and personal digital assistant, touch-sensitive displays, and circuit memory -- aren't new ideas.

Apple filed a lawsuit against Qualcomm last year, which sparked off countersuits by Qualcomm. The US International Trade Commission is currently considering one case, involving whether iPhones containing chips from Qualcomm rival Intel should be banned from the US for infringing a Qualcomm patent. Last week, the ITC said Apple has infringed at least one of Qualcomm's patents.

Qualcomm has created technology that's essential for connecting phones to cellular 3G and 4G networks. The company derives a significant portion of its revenue from licensing those inventions to hundreds of device makers, with the fee based on the value of the phone, not the components. Any handset maker building a device that connects to the cellular networks has to pay the company a licensing fee, even if it doesn't use Qualcomm's chips.

Apple claims that Qualcomm is wrong and that it shouldn't have to pay as much for licensing Qualcomm technology.