US and European regulators gave the green light on Monday to Internet giant Google's $12.5 billion acquisition of Motorola Mobility.

In a related decision, the Justice Department's antitrust division also approved the purchase by Apple, Microsoft and Research In Motion (RIM) of patents from Nortel Networks and the acquisition by Apple of Novell patents.

The Justice Department said it examined the three deals simultaneously to determine ‘whether the acquiring firms could use these patents to raise rivals' costs or foreclose competition’.

"After a thorough review of the proposed transactions, the Antitrust Division has determined that each acquisition is unlikely to substantially lessen competition and has closed these three investigations," it said.

"The division concluded that the specific transactions at issue are not likely to significantly change existing market dynamics," it said.

Google acquired 17,000 patents with the purchase of Motorola Mobility and has been strengthening its patent portfolio as the fight for dominance in the booming smartphone and tablet computer market increasingly involves lawsuits claiming infringement of patented technology.

Apple and South Korea's Samsung, whose devices are powered by Google's Android software, are currently involved in lengthy and costly patent fights being waged on several continents.

In announcing the Motorola Mobility 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 Justice Department said it had focused its investigation on the licensing of standard essential patents, or SEPs.

"During the course of the division's investigation, several of the principal competitors, including Google, Apple and Microsoft, made commitments concerning their SEP licensing policies," it said.

"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, as well as their commitments not to seek injunctions in disputes involving SEPs," it said.

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

The antitrust division said it will monitor the use of SEPs in the smartphone and tablet markets and ‘will not hesitate to take appropriate enforcement action to stop any anticompetitive use of SEP rights’.

The Justice Department's green light for the Google-Motorola Mobility deal came just hours after European Union regulators announced their approval.

"We have approved the acquisition of Motorola Mobility by Google because, upon careful examination, this transaction does not itself raise competition issues," said Joaquin Almunia, the EU's antitrust commissioner.

The EU investigation centered on whether Google might make it harder for handset manufacturers such as Samsung or Taiwan's HTC to use Android once it owns Motorola Mobility, which also makes smartphones and tablet computers.

"It is unlikely that Google would restrict the use of Android solely to Motorola, a minor player in the European Economic Area," the Commission said.

Welcoming the European Commission approval, Google deputy general counsel Don Harrison said, "The combination of Google and Motorola Mobility will help supercharge Android.

"It will also enhance competition and offer consumers faster innovation, greater choice and wonderful user experiences," Harrison said in a blog post.