TOKYO - Nippon Steel said on Friday it will sell its entire 50% stake in a joint venture steel plant it has in Calvert, Alabama, with ArcelorMittal , if the top Japanese steelmaker's buyout bid for United States Steel is successful.

Nippon Steel's planned purchase of U.S. Steel has faced political opposition since it was signed last December. U.S. Vice President and Democratic presidential candidate Kamala Harris and Republican challenger Donald Trump both say they support keeping U.S. Steel as an American-owned company.

The Committee on Foreign Investment in the United States (CFIUS) has extended its review of the deal until the end of December, or until after the U.S. presidential elections in early November, and Nippon Steel has resubmitted its application to CFIUS.

Nippon Steel said on Friday the proposed share transfer in the joint venture in Alabama is aimed at "proactively address any antitrust concerns" that could arise from Nippon Steel's ongoing ownership in the plant after the U.S. Steel deal.

"Nippon Steel has determined that the share transfer is the most assured path to receiving timely regulatory approval for the acquisition," it said in a statement, adding its plan of closing the U.S. Steel deal by the year-end was unchanged.

Nippon Steel would book a consolidated loss of about 230 billion yen ($1.55 billion) upon its sale of the NS Kote holding company that owns the joint venture stake in the Calvert plant to ArcelorMittal for $1, the company said.

If the acquisition of U.S. Steel is not completed for any reason, the sale of NS Kote in Alabama to ArcelorMittal "will not be consummated and there will be no impact on earnings performance," Nippon Steel said in its statement.

($1 = 148.7400 yen)

(Reporting by Kantaro Komiya and Katya Golubkova; Editing by Christian Schmollinger and Tom Hogue)