The European Commission is now investigating a total of nine antitrust complaints against Internet search engine giant Google, two sources said on Tuesday.

The EU antitrust regulator has up to now only confirmed four cases against Google.

"The Commission has nine formal complaints now. The new complaints come from small companies," said one of the sources who declined to provide details because of the sensitivity of the matter.

The second source said three cases came from national regulators while two were fresh complaints.

The EU antitrust regulator opened a case against Google in November last year following allegations by three small companies that the Google demoted their sites in Web search engines because they were rivals.

Microsoft followed four months later with its first-ever complaint to the EU watchdog, claiming that Google systematically blocked Internet search competition.