Amazon has revealed that 11 companies have filed patent lawsuits against it since the start of the year – more than three times as many as in all of 2010.

The online store made the declaration in a filing to US financial regulators.

The complaints include claims that Amazon’s sales systems infringe another firm’s intellectual property, and that its Kindle ebook devices use technologies owned by two others.

Amazon says it disputes the claims and intends to “vigorously defend” itself.

The US firm’s filing reveals that it has been accused of infringing a total of 30 patents since January.

Of those two have been dismissed, including a claim by MasterObjects, a Dutch developer specialising in search result software.

The software firm had claimed that Amazon’s drop-down search suggestions infringed one of its US patents. However, the case was thrown out in August.

One of the active lawsuits involves a company named LVL Patent Group. It claims Amazon’s mobile applications and other technologies breach four of its innovations.