U.S. President Donald Trump on Monday reiterated his firm opposition to foreign ownership of U.S. Steel, casting renewed doubt on Japanese conglomerate Nippon Steel’s proposed $15 billion acquisition of the iconic American manufacturer.

Speaking at a press briefing, Trump emphasized the need to maintain domestic control over strategically vital industries.

“U.S. Steel must remain under American ownership,” Trump said. “We will not allow foreign interests to take control of a company so central to our economic and national security.”

The president’s remarks echoed statements made last week that caused U.S. Steel shares to fall more than 7%, amid growing investor concerns that the deal could be blocked on political grounds.

Despite the turbulence, both U.S. Steel and Nippon Steel issued a joint statement late Monday, indicating that negotiations with the U.S. administration remain ongoing.

“We are actively working with government stakeholders to ensure the transaction supports American jobs and manufacturing,” the companies said.

The acquisition has become a flashpoint in U.S.-Japan trade discussions. President Trump and Japanese Prime Minister Shigeru Ishiba reportedly addressed the deal during their February meeting, though no public consensus was reached at the time.

Industry analysts say Trump’s stance reflects broader concerns about foreign control of key U.S. infrastructure, especially in a politically charged election year. The deal, which would be one of the largest foreign takeovers of a U.S. industrial firm in decades, still faces review by the Committee on Foreign Investment in the United States (CFIUS).