WASHINGTON (Kyodo) -- U.S. President-elect Donald Trump reiterated Monday that he will prevent Nippon Steel Corp. from acquiring United States Steel Corp., vowing to block the deal soon after returning to the White House next month.

"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 said on his Truth Social platform.

The post came as the leading Japanese steelmaker hopes to complete its planned purchase of the U.S. producer by the end of the year, with Trump taking office on Jan. 20.

"Through a series of Tax Incentives and Tariffs, we will make U.S. Steel Strong and Great Again, and it will happen FAST!" he said. "As President, I will block this deal from happening. Buyer Beware!!!"

During the presidential race, Trump pledged that if elected he would block the acquisition deal agreed by the two steelmakers' managements, which is worth more than $14 billion.

In response to Trump's remarks, Nippon Steel issued a statement reiterating the importance of the acquisition, saying it "will not only help U.S. Steel grow but also strengthen the national security of the United States."

Touching on its plan to invest at least $2.7 billion in the U.S. company's facilities, Japan's largest steelmaker also said, "We will introduce Nippon Steel's technology so that U.S. employees can provide cutting-edge steel products to American customers. We will also protect jobs."

Japanese Prime Minister Shigeru Ishiba declined to comment on Nippon Steel's acquisition plan during a parliamentary session, calling it "an individual company's business." At the same time, he emphasized the importance of the two countries boosting economic cooperation through bilateral investment.

U.S. Steel's shareholders have also backed the takeover, which is aimed at making it more globally competitive and would create the world's third-largest steelmaker by volume.

But the proposed merger has been opposed by the powerful United Steelworkers union, headquartered in Pennsylvania, which was a key battleground state in the presidential election.

With labor union votes deemed vital in paving the path to the White House, President Joe Biden and Vice President Kamala Harris, who was defeated by Trump in the Nov. 5 election, were also against the deal, which was announced in December last year.

The U.S. Committee on Foreign Investment is reviewing the proposed acquisition until late December.

The committee, also known as CFIUS, which is chaired by Treasury Secretary Janet Yellen, is in charge of examining whether foreign investment transactions involving U.S. companies pose a threat to national security.

U.S. Steel, founded in 1901, is also based in Pennsylvania, which Trump won along with all six other swing states. The company was once a symbol of American economic prowess, but it has struggled to keep up with competition from foreign rivals. It ranked 24th globally last year, according to World Steel Association data.