WASHINGTON— Google Inc. said European antitrust authorities have opened a preliminary inquiry into complaints about its tactics made by three European Internet companies.

The inquiry, disclosed late Tuesday, appears to focus largely on complaints that Google unfairly ranks the sites of the Internet competitors, in effect lowering their rank in search results that appear on Google sites.

Google denied violating European law or taking any action to stifle competition.

The European Commission inquiry is at an early, fact-finding stage and may not result in any action. But it appeared to be the first time that European antitrust authorities have examined Google's conduct outside of a merger review. The inquiry also comes at a time of heightened scrutiny of Google in Europe, where the company has an even more dominant position in search advertising than it does in the U.S.

Google said the allegations were made by Ciao.de, a German subsidiary of Microsoft Corp. , Foundem.co.uk, a U.K. price comparison site, and EJustice.fr, a French site specializing in legal search inquiries. Foundem and EJustice could not immediately be reached for comment.