Microsoft on Wednesday filed a complaint with the European Commission against Google's Motorola Mobility in the latest salvo in an increasingly bitter patent war between technology giants.

Apple, which is embroiled in a multi-continent patent fight with South Korea's Samsung, lodged a similar complaint against Motorola Mobility with European competition regulators last week.

Both Microsoft and Apple accuse Motorola Mobility, which is being acquired by Google for $12.5 billion, of unfairly using its patent portfolio to try to block competing products.

At issue are what are known as standard essential patents. SEPs are patents that have been identified by technology companies as necessary to allow them to build compatible products.

Motorola Mobility is failing to live up to an industry pledge to license SEPs to rivals on fair, reasonable and nondiscriminatory terms, according to Microsoft and Apple.

"Motorola is attempting to block sales of Windows PCs, our Xbox game console and other products," Microsoft deputy general counsel Dave Heiner said, explaining the software giant's decision to file a complaint with the EC.

"Motorola is demanding that Microsoft take its products off the market, or else remove their standards-based ability to play video and connect wirelessly," Heiner said in a blog post.

"(Motorola Mobility) is on a path to use standard essential patents to kill video on the Web, and Google as its new owner doesn't seem to be willing to change course," he said.

US and European regulators gave the green light last week to Google's acquisition of Motorola Mobility.

Google, whose Android software is used by smartphone and tablet computer makers, acquired 17,000 patents with the purchase of the Illinois-based maker of mobile phones, tablet computers and television set-top boxes.

Announcing the acquisition in August, Google chief executive Larry Page said it will "enable us to better protect Android from anti-competitive threats from Microsoft, Apple and other companies."

The US Justice Department's antitrust division, in approving the Google-Motorola Mobility deal, said Google, Apple and Microsoft had made commitments concerning their SEP licensing policies.

"The division's concerns about the potential anticompetitive use of SEPs was lessened by the clear commitments by Apple and Microsoft to license SEPs on fair, reasonable and non-discriminatory terms," it said.

Google's commitments, however, "were more ambiguous and do not provide the same direct confirmation of its SEP licensing policies," the department said.

Heiner said Motorola Mobility "has refused to make its patents available at anything remotely close to a reasonable price.

"For a $1,000 laptop, Motorola is demanding that Microsoft pay a royalty of $22.50 for its 50 patents on the video standard," he said, while a group of 29 companies was making 2,300 other patents available for just two cents.

"If every firm priced its standard essential patents like Motorola, the cost of the patents would be greater than all the other costs combined in making PCs, tablets, smartphones and other devices," Heiner said.

Microsoft was not using SEPs in an attempt to block smartphones or tablets running Android, Heiner said, and he appealed to Google to change course.

"For a company so publicly committed to protecting the Internet, one might expect them to join the growing consensus against using standard essential patents to block products," he said.

Patent analyst Florian Mueller said on his FOSS Patents blog he expected the EC to "make a determination on the launch of full-blown investigations within a few months."

Mueller adde
d that "if every owner of standard-essential patents behaved like Motorola, this industry would be in chaos, and grind to a halt.

"It's key that the owners of such patents act responsibly, and if some of them don't, antitrust intervention is needed," he said.

"I don't dispute any company's right to defend its intellectual property vigorously, but when standard-essential patents are involved, there must be clear limits."