Internet giant Google launched a flight search tool on Tuesday in a potential challenge to online travel services.

Flight Search is the first travel product from Google since its US$700 million acquisition of ITA Software earlier this year.

"Since then, our engineering teams have been working closely together to build new travel tools that provide faster, more flexible, and more useful results to online travel searches," Google said in a blog post.

A "Flights" link will appear on the left-hand side of the page when a Google search user types in a query for flight information. Flight Search can also be directly accessed through google.com/flights.

For the moment, Flight Search only offers flights for a limited number of U.S. cities and shows results for round-trip economy-class flights only.

Google said it will add more cities and options later.

Flight Search shows flight options for a selected destination organized by departure time and date, airport, price or airline.

Google, which required the approval of the U.S. Justice Department for the ITA purchase, said the selection of flight results "is not influenced by any paid relationships."

"Airlines control how their flights are marketed, so as with other flight search providers, our booking links point to airline websites only," Google said.

Several online travel sites, including Expedia, Kayak and Travelocity, had sought to block the Google-ITA deal, claiming it would give Google too much control over the lucrative online travel market and lead to higher prices.

The Justice Department's anti-trust division approved the acquisition of ITA by Google in April but imposed conditions on the deal, including requiring Google to continue to license ITA's travel software to other companies.

ITA, a 500-person firm founded in 1996 by Massachusetts Institute of Technology computer scientists, specializes in organizing airline data, including flight times, availability and prices.

ITA flight data software is used by many U.S. airlines and a number of leading online travel sites, including Expedia's Hotwire and TripAdvisor, Kayak, Orbitz and Microsoft's Bing search engine.

In July, Google launched Hotel Finder which it described as an "experimental search tool" designed to help users locate and book hotels.

Hotel Finder, which is restricted to the United States for now, lets a user refine their choice by geographic area using Google Maps and select hotels using various criteria including price, the number of stars and user ratings.