The EU slapped Google with anti-trust charges on Wednesday over its widely-used Android mobile phone operating system, in a fresh salvo by Brussels against the Silicon Valley giant.

Competition Commissioner Margrethe Vestager said Google had used practices such as making manufacturers pre-install its search engine as the default in order to preserve its market dominance.

"The preliminary conclusions from our investigations is that these practices breach EU competition law," Vestager told a press conference, adding that Brussels believed that "Google has abused its dominant position"

She added: "We have found that Google pursues an overall strategy on mobile devices to protect and expand its dominant position in Internet search."

European Commissioner for Competition Margrethe Vestager, pictured on January 11, 2016, all but confirmed that her team was ready to target Google over its dominance of the mobile phone industry. Photo: AFP

The charges are a massive blow to one of the Google's most strategic businesses that could alter a global smartphone sector that is fast taking over traditional PC's as the biggest segment in the world of computing.

The EU in its charge sheet accused Google of obstructing innovation by giving unfair prominence to its own apps, especially its search engine, in deals with mobile manufacturers such as Samsung or Huawei.

Google is also accused of restricting manufacturers from installing rival operating systems on their phones.

The Android operating system captures about 80 percent of the world market for mobile phones, far ahead of its closest rival Apple.

The case is the second attack by the EU against Google. Last year, the EU formally charged the company for abusing its dominance of the search engine market in Europe.

In both cases, Google risks a fine of 10 percent of worldwide global sales for one year, which would amount to a $7.4 billion fine on the basis of 2015 revenues.

The EU is looking at whether Google gives unfair prominence to its own apps such as maps or music streaming in deals with mobile manufacturers such as Samsung or Huawei. Photo: AFP

Google said it would work with the EU to show that consumers benefitted from Android.

"Android has helped foster a remarkable -- and, importantly, sustainable -- ecosystem, based on open-source software and open innovation," Kent Walker, Senior Vice President and General Counsel of Google, said in a statement.

"We look forward to working with the European Commission to demonstrate that Android is good for competition and good for consumers."