European regulators opened Tuesday two antitrust investigations against Motorola Mobility, bought by US Internet giant Google, in the latest chapter of an escalating patent war with Apple and Microsoft.

The European Commission said it would check whether Motorola had abused a dominant market position on patents by seeking injunctions to stop Apple and Microsoft from selling their iPhone, iPad, Xbox and Windows products.

Microsoft and Apple accuse Motorola Mobility of unfairly using its extensive patent portfolio to try to block competing products through court orders across the EU and by charging excessive licensing prices for essential patents.

In February, European Union and US regulators cleared the acquisition of Motorola Mobility for $12.5 billion (9.4 billion euros) by Google.

The battle is centered on standard essential patents (SEP) that technology companies must make available to rivals at a reasonable price because they are vital to the functioning of certain products.

Microsoft and Apple claim that Motorola Mobility is failing to live up to an industry pledge to license SEPs to rivals on so-called fair, reasonable and nondiscriminatory (FRAND) terms.

Motorola made FRAND commitments to standard setting organisations for 2G and 3G mobile and wireless telecommunications, H.264 video compression and WLAN technologies.

The commission said it would assess whether Motorola Mobility "has abusively, and in contravention of commitments it gave to standard setting organisations, used certain of its standard essential patents to distort competition in the Internal Market in breach of EU antitrust rules."

It added: "The Commission will examine whether Motorola's behaviour amounts to an abuse of a dominant market position."

The European Union's executive arm said it would also assess allegations by Apple and Microsoft that "Motorola offered unfair licensing conditions for its standard-essential patents in breach" of antitrust rules.

Brussels had already opened in late January a similar case against South Korea's Samsung Electronics, which is embroiled in a multi-continent patent fight with Apple.

The European Commission is investigating whether Samsung went too far last year when it sought injunctions against mobile device competitors in various EU national courts, alleging infringements of Samsung's patent rights.

Google, whose Android software is used by smartphone and tablet computer makers, acquired 17,000 patents with the purchase of the Illinois-based Motorla, 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."

European Commission spokesman Antoine Colombani said the investigation is looking into "past and current behaviour" of Motorola but indicated it did not include Google since the acquisition has yet to be completed.

"We haven't finalised our acquisition of Motorola Mobility but will work with the European Commission to answer any questions they might have," Al Verney, a Google spokesman, told AFP.

Google already has "longstanding concerns" about patent abuses, including lawsuits and royalty demands targeting the Android system, he added.

Google is facing a separate EU antitrust probe over its search engine, with travel websites Expedia and TripAdvisor on Tuesday joining 11 companies in a complaint claiming that the US company was rigging the online search market.