RALEIGH, North Carolina (Reuters) - U.S. Treasury Secretary Janet Yellen on Thursday that the U.S. welcomes foreign direct investment and rigorously reviews deals for national security concerns, but declined to comment on reports that President Joe Biden's administration is poised to block the U.S. Steel-Nippon Steel merger.

Speaking to reporters in North Carolina, Yellen said the ultimate decision on national security decisions on foreign acquisitions rests with Biden.

On Wednesday, Reuters and other news outlets reported that the Biden administration was poised to block Nippon Steel's $14.9 billion acquisition of U.S. Steel on national security grounds.

Reuters reported that the administration told Nippon Steel in a letter on Saturday that the merger would pose a national security risk by harming the American steel industry, citing three people familiar with the notice.

The deal faces opposition from numerous Democrats and Republicans, with Vice President and Democratic presidential candidate Kamala Harris saying on Monday she wants U.S. Steel to remain "American owned and operated." Her Republican rival Donald Trump has pledged to block the deal if elected.

Asked about the matter, Yellen said: "The United States has the environment in which we very much welcome foreign direct investment. We're seeing a huge amount of it in firms in North Carolina that have been here for a long time and coming in response to the Inflation Reduction Act."

She also said the U.S. has a "rigorous" review process for national security implications of deals.

"That's a process that is intended to advise the president, who makes the ultimate decisions on this," she said.