European Union regulators are investigating whether Samsung Electronics breached antitrust rules in its legal battles against rivals, among them Apple, which use its mobile technology patents.

South Korea's Samsung, the world's top maker of smartphones, is involved in a patent tussle with Apple in 10 countries including the United States, Australia, France and Japan.

Apple is also Samsung's biggest customer.

Last year, Samsung sought injunctions in various EU countries against competitors, saying they infringed some of its patent rights, which it has declared essential to implement European mobile telephony standards.

Samsung pledged in 1998 to license its patents to the European Telecommunications Standards Institute on fair, reasonable and non-discriminatory (FRAND) terms.

The (European) Commission will investigate, in particular, whether in doing so (seeking injunctions on patent infringements in 2011) Samsung has failed to honor its irrevocable commitment given in 1998 to the European Telecommunications Standards, the EU executive said.

It said it would investigate whether Samsung was abusing its dominant position through such actions.

Samsung's main competitors in the mobile device market are Apple, Finland's Nokia and Blackberry maker, Canada's Research in Motion, as well as other makers of phones using Google's Android software.

(Reporting by Foo Yun Chee and Jan Strupczewski; Editing by Rex Merrifield and Erica Billingham)