Microsoft is to file a complaint against Google to European competition authorities, alleging it abuses its dominant position in the search market in the region.
Microsoft claims Google is using technical measures to restrict rival search engines from indexing content on Google-owned video-sharing site YouTube, and preventing Microsoft smartphones from working with YouTube.
The complaint is likely to be added to the European Commission's investigation into anti-competitive practices by Google, which was started in November 2010, according to the BBC.
The allegations come as Microsoft continues to struggle to gain market share despite an estimated investment of $1bn in development and advertising, says Mike Davis, analyst at Ovum.
The total value of internet advertising is huge, he says, and this is a territory that both Google and Microsoft need to dominate.
"Irrespective of the eventual EC adjudication, this war will continue for a long time yet," says Davis.