The U.S. Justice Department has filed a lawsuit seeking to stop Anheuser-Busch Inbev SA from buying the half of Mexican brewer Grupo Modelo that it does not already own.

The department said that the $20.1 billion deal would lessen competition in the U.S. beer market.

"If ABI fully owned and controlled Modelo, ABI would be able to increase beer prices to American consumers. This lawsuit seeks to prevent ABI from eliminating Modelo as an important competitive force in the beer industry," Bill Baer, assistant attorney general in charge of the Department of Justice's Antitrust Division, said in an emailed statement.

(Reporting By Diane Bartz; editing by Ros Krasny)