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Google has accused rivals Microsoft and Apple of buying up technology patents in a bid to hold back Android.

In a blog post, one of Google's top lawyers accused the firms of using "bogus patents" to crank up the cost of Android-powered devices.

Microsoft hit back saying Google had been invited to bid with it on key patents but turned down the chance.

The statement comes after Google lost several battles over patents covering technology used in handsets.

, entitled "When patents attack Android", Google's chief legal officer David Drummond said Android's success had driven its rivals to unite and wage a "hostile, organized campaign" against the mobile operating system.

The conflict was being fought through patents, he said, and paying to licence those patents amounted to a "tax" on Android.

Rivals were seeking to consolidate their position by buying up more patents to stop Google getting hold of them, said Mr Drummond.

In recent months Google has lost auctions for thousands of patents owned by Novell and Nortel, many of which relate to technologies that can be used in smartphones. Ownership of those patents went to consortia made up of many tech firms including Apple and Microsoft.

"Patents were meant to encourage innovation, but lately they are being used as a weapon to stop it," he wrote.

The blog post drew a swift reaction from Brad Smith, Microsoft's top lawyer, who disputed Mr Drummond's recollection of events.

: "Google says we bought Novell patents to keep them from Google. Really? We asked them to bid jointly with us. They said no."

Soon after Frank Shaw, Microsoft's head of communications, Google lawyer Kent Walker which demonstrated that Google had turned down the chance to join its bid on the Novell patents.

Patent expert Florian Mueller said the blog post expressed Google's "frustration" and he added that the fact that Google controlled relatively few patents covering mobile technology had become a "strategic issue".

"The price of Android phones could go up and the other aspect of this is that there could possibly be degradations of the user experience," he said.

While many firms are happy to issue licences for patents they own others do not. Apple, said Mr Mueller, often denies rivals the chance to use the technologies it owns patents for in other devices.

Google alluded to this practice in its blog post saying it was keen for Android to be a "competitive choice". If it is blocked from employing some features then Android devices may be less easy to use than those of more established rivals.

"Google should acquire more patents," said Mr Mueller. "Their big mistake was not to get into the patent buying business. They should have foreseen this."

be related to acquisition target InterDigital which is known to own more than 8,000 patents many of which relate to mobile technologies.

Google is known to be interested in acquiring InterDigital but could face competition from Apple, Microsoft and many others. While Google has billions of dollars on hand to finance its bid for InterDigital, the combined might of its rivals may prove hard to beat.