TOKYO (Reuters) -Japan's Nippon Steel ( NISTF ) on Monday declined to comment on U.S. President Donald Trump saying that no one can have a majority stake in acquisition target U.S. Steel.

Trump made the comment on Sunday when speaking to reporters on Air Force One. He also said the U.S. will impose 25% tariffs on all steel and aluminium imports on top of existing duties, and that he will announce the new metals tariffs on Monday.

Shares in Nippon Steel ( NISTF ) fell more than 2% in early trade, compared with a 0.3% decline in the Nikkei index.

On Friday, Trump said Nippon Steel's ( NISTF ) $14.9 billion bid for U.S. Steel would take the form of an investment instead of a purchase. Two people familiar with the matter said the Japanese biggest steelmaker had not withdrawn its bid.

Nippon's pursuit of U.S. Steel has stretched on for more than a year, with Trump condemning the proposal on numerous occasions, before Friday's more tempered remarks at the Oval Office with Japanese Prime Minister Shigeru Ishiba at his side.

It was unclear if the investment referred to a new deal structure or what the details of the transaction would be, but Trump said on Friday he would meet with the head of Nippon Steel ( NISTF ) this week and he would be involved "to mediate and arbitrate".

Ishiba, on returning from the U.S., told broadcaster Nippon TV on Sunday that there are legal questions regarding the distinction between acquisition and investment, including the extent of stock ownership.

He said such details are likely to be discussed between Trump and Nippon Steel ( NISTF ).

"The key point is whether Americans will feel that U.S. Steel will remain an American company," Ishiba said.

Nippon Steel ( NISTF ) on Monday declined to issue a statement on Ishiba's comments or any management meeting with Trump.

Nippon Steel's ( NISTF ) bid for U.S. Steel is central to the Japanese company's global expansion plan. It was blocked last month by then-U.S. President Joe Biden citing national security.

The firm, together with U.S. Steel, filed a number of lawsuits challenging Biden's decision.

Nippon Steel ( NISTF ) Vice Chairman Takahiro Mori last week said the Japanese company had no plan to change the acquisition structure.