SAN FRANCISCO - Google CEO Sundar Pichai on Wednesday challenged the 5-billion-US-dollar antitrust fine that the European Commission has slapped on the world's Internet leader for competition breach, and vowed to appeal the case.

Pichai denied the European Commission charge that Google has restricted competition and forced smartphone manufacturers to install Google search and browser apps on the Android operating system developed by Google.

The European Commission said it was fining the US tech giant for "three types of restrictions that (it) has imposed on Android device manufacturers and network operators to ensure that traffic on Android devices goes to the Google search engine."

However, Pichai argued that the European Commission allegation was not true, saying "rapid innovation, wide choice, and falling prices are classic hallmarks of robust competition."

"Android has enabled this and created more choice for everyone, not less. This is why we intend to appeal today's Android decision," he tweeted on Wednesday.

"The Commission's Android decision ignores the new breadth of choice and clear evidence about how people use their phones today," the Google CEO also wrote in a blog post the same day.

He said the decision ignores the fact that "Android phones compete with iOS phones, something that 89 percent of respondents to the Commission's own market survey confirmed."

Without rules around baseline compatibility, open-source platforms fragment, which hurts users, developers and phone makers, but Android's compatibility rules avoid this and help make it an attractive long-term proposition for everyone, Pichai said.

"Last year, over 94 billion apps were downloaded globally from our Play app store; browsers such as Opera Mini and Firefox have been downloaded more than 100 million times, UC Browser more than 500 million times," he wrote.

The fine, which came after a three-year probe, is the biggest punishment that the European Union has ever handed down on a company for anticompetitive practices.

The EU regulator asked Google to bring its "illegal conduct to an end in an effective manner within 90 days of the decision."

Google was fined a record-breaking 2.7 billion dollars by the EU last year for alleged manipulating search results, a case also being appealed by the US Internet giant that is expected to last for years.

Other US tech behemoths such as Microsoft, Facebook and Intel have all faced similar anti-competition fines from the EU regulator.