June 9 (Reuters) - The U.S. Federal Trade Commission has sought information from some of the world's top advertising firms as part of a probe into whether advertising and advocacy groups violated antitrust laws by coordinating boycotts of certain sites, the Wall Street Journal reported.

Omnicom OMC.N, WPP WPP.L, Dentsu 4324.T, Interpublic Group IPG.N and Publicis Groupe PUBP.PA are among the agencies that the FTC sent letters to on Monday.

Reuters could not immediately verify the report.

(Reporting by Pretish M J in Bengaluru; Editing by Rashmi Aich)

((PretishMJ@thomsonreuters.com; +91 8056974974;))