U.S. President-elect Donald Trump said on Monday a series of tax incentives and tariffs will revive storied American firm U.S. Steel, as he reiterated his opposition to Nippon Steel's planned $15 billion purchase of the company.

"I am totally against the once great and powerful U.S. Steel being bought by a foreign company, in this case Nippon Steel of Japan," Trump wrote on his social-media platform Truth Social.

"I will block this deal from happening. Buyer Beware!!!"

Nippon Steel hopes to close the deal before Trump retakes the White House on January 20, despite opposition from President Joe Biden and a powerful U.S. labor union.

Last week, Japanese Prime Minister Shigeru Ishiba wrote to Biden, who has referred the deal to a government panel that reviews foreign investments for national security risks, asking him to approve the transaction, sources have said.

The deadline for that Committee on Foreign Investment in the United States (CFIUS) review is next month. CFIUS could approve the deal, possibly with measures to address national security concerns, or recommend that the president block it. It could also extend the review.

(Reporting by Costas Pitas; Editing by Michelle Price and Edwina Gibbs)