Tokyo, Japan - Nippon Steel on Wednesday slammed the "inappropriate" influence of politics on its planned takeover of US Steel after President Joe Biden was reportedly ready to block it.

The deal worth $14.9 billion including debts is being reviewed by the Committee on Foreign Investment in the United States (CFIUS), helmed by Treasury Secretary Janet Yellen.

Bloomberg News, citing people close to the matter, said Biden planned to kill the sale on national security grounds when the review is finished later this month.

"It is inappropriate that politics continue to outweigh true national security interests – especially with the indispensable alliance between the US and Japan as the important foundation," a Nippon Steel statement said.

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"We have engaged in good faith with all parties to underscore how the transaction will bolster American economic and national security by countering the threats posed by China," it added.

"Nippon Steel still has confidence in the justice and fairness of America and its legal system, and – if necessary – will work with US Steel to consider and take all available measures to reach a fair conclusion."

The takeover was agreed by the companies around a year ago. US Steel says it needs the Nippon deal to ensure sufficient investment in plants in Pennsylvania, which it warns it may have to shutter if the sale is blocked.

But the buyout has been fiercely condemned by the United Steelworkers union, despite Nippon's promises of investments to keep Pennsylvania factories competitive and newer "mini mills" in the American South.

After the deal was first announced, Biden said it was "vital" that US Steel be "domestically owned and operated."

"I told our steelworkers I have their backs, and I meant it," he insisted in March.

President-elect Donald Trump – who will be inaugurated on January 20 – has also vowed to block the deal, pledging to bolster US Steel through tax incentives and tariffs instead.

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"I am totally against the once great and powerful U.S. Steel being bought by a foreign company," Trump wrote earlier this month on his Truth Social platform.

"The president's position since the beginning is that it is vital for US steel to be domestically owned and operated," White House spokesperson Robyn Patterson said. "We have not received any CFIUS recommendation. The CFIUS process was and remains ongoing."