Google faced another regulatory challenge on Monday when the authorities in Turkey opened an investigation into whether the search giant's popular Android software had broken the country's antitrust rules.

The investigation in Turkey is the latest legal problem for Google, which faces three separate competition charges in Europe and has already been found to breach antitrust legislation in Russia. United States officials have also investigated the company over its Android and search services, but they have not brought a case.

Google denies that it has broken any laws, saying that its digital services like search and online maps do not hinder those of rivals.

The number of regulatory investigations worldwide represents a growing threat for the company, just as other Silicon Valley giants like Facebook and Amazon increasingly challenge Google in the race to create new tech gadgets and digital services.