UPDATE 1-US judge says Google must face some advertisers' antitrust claims, dismisses others

(Adds details of ruling)

March 1 (Reuters) - Alphabet's Google must face advertisers' proposed class action lawsuit claiming that it monopolizes the ad exchange market, a U.S. judge ruled on Friday.

But U.S. District Judge Kevin Castel dismissed some other antitrust claims, including those focused on ad-buying tools used by large advertisers.

Castel was reviewing a number of cases against Google, and his decision struck down many claims but allowed at least one key set to proceed.

The advertisers, he wrote, "have not plausibly alleged antitrust standing in the markets for ad-buying tools used by large advertisers, but they plausibly allege antitrust standing as to injuries they purportedly suffered from anti-competitive practices in the ad-exchange market and the market for small advertisers' buying tools."

Castel also said Gannett, the largest U.S. newspaper chain and publisher of USA Today, could try in a separate case to prove that Google fraudulently concealed anticompetitive effects of some technology. Gannett alleged that it sold some of its ad space directly to advertisers, but Google still made the inventory available for auction on its ad exchange in order to accrue transaction fees for its own benefit.

Google and Gannett did not immediately respond to requests for comment.

The judge also ruled in multiple other cases in the nationwide litigation.

Google faces a number of claims on antitrust grounds.

The U.S. Justice Department sued Google in January 2023, accusing it of abusing its dominance in digital advertising. The government asked for the divestiture of the Google Ad Manager suite, including Google's ad exchange, AdX.

Google Ad Manager is a suite of tools including one that allows websites to offer advertising space for sale and an exchange that serves as a marketplace that automatically matches advertisers with those publishers.

Advertisers and website publishers have complained that Google has not been transparent about where ad dollars go, specifically how much goes to publishers and how much to Google. (Reporting By Jon Stempel and Sheila Dang; editing by Peter Henderson and Leslie Adler)