Google is working behind the scenes to protect its Android platform from patent lawsuits.

The Internet search giant sold nine patents to HTC last week to help the handset manufacturer defend itself in an ongoing patent battle with Apple, according to U.S. Patent and Trademark Office records first obtained by Bloomberg.

HTC cited the patents in an amended complaint filed Tuesday with a Delaware district court.

Google reportedly bought the patents less than a year ago from Motorola, Openwave and Palm.

Google and HTC could not be immediately reached for comment.

The added intellectual property will give HTC additional ammunition against Apple, which is suing the company on multiple fronts over its Android-based smartphones and tablets. Apple alleges HTC's devices violate several of its patents on wireless technology. HTC is contesting the charges and has filed countersuits against Apple.

The companies' patent war spans multiple courts, including the International Trade Commission.

Google has struggled to defend Android against an onslaught of patent suits from its competitors, namely Apple and Microsoft. The company has alleged that is rivals are using patents to wage a "hostile, organized campaign against Android."

"Android's success has yielded something else: a hostile, organized campaign against Android by Microsoft, Oracle, Apple and other companies, waged through bogus patents," Google chief legal officer David Drummond said in a post on the company's official blog earlier this summer.

Google attempted to shore up its patent rights with a bid on Nortel's intellectual property portfolio, but was ultimately outbid by a group of tech companies including Apple and Microsoft. The failed Nortel bid spurred Google's $12.5 billion purchase of Motorola Mobility this summer. Motorola holds 17,000 patents and 7,500 pending patent applications worldwide.

HTC has also snapped up patents in an effort to defend itself in court. In July, the company agreed to pay $300 million for S3 Graphics, which holds 235 patents and patent applications.