The war of words is escalating quickly between Microsoft and Google over patents and Android.

Microsoft’s general counsel responded this afternoon to a withering blog post from his Google counterpart that accused the Redmond company of getting in bed with Apple to use questionable patents to undermine Google’s Android mobile operating system.

Posted Microsoft’s Brad Smith on Twitter: “Google says we bought Novell patents to keep them from Google. Really? We asked them to bid jointly with us. They said no.”

That was a reference to an effort by a consortium led by Microsoft to acquire Novell’s patents. They ultimately ended up entering into a licensing deal instead, after the Department of Justice raised objections.

In his blog post earlier today, Google’s David Drummond cited the Novell patent bid as one example of “a hostile, organized campaign against Android by Microsoft, Oracle, Apple and other companies, waged through bogus patents.” He also pointed to Microsoft’s patent lawsuits against Android device makers, and its broader effort to extract patent royalties on Android devices.

Here’s an email that, according to Microsoft, shows Google turning down the invitation. (Click to enlarge.)