DOVER, Delaware Sept 27 (Reuters) - U.S. President Joe

Biden said on Friday his opposition to Nippon Steel's ( NISTF )

$14.9 billion bid for U.S. Steel hadn't changed despite a

decision by his administration to extend a national security

review of the proposed tie-up.

"I haven't changed my mind," he told reporters, when asked

if the extension indicated a change of heart.

Nippon Steel ( NISTF ) and U.S. Steel did not immediately respond to

requests for comment.

The remarks threw cold water on hopes by deal supporters

that the proposed tie-up could get a green light from the

Committee on Foreign Investment in the United States, which

reviews foreign investments for national security risks.

The proposed merger appeared set to be blocked when

CFIUS alleged on Aug. 31 the transaction posed a risk to

national security by threatening the steel supply chain for

critical U.S. industries, as exclusively reported by Reuters.

But a move reported by Reuters earlier this month to

delay a decision on the politically sensitive merger until after

the Nov. 5 presidential election gave hope to proponents of the

tie-up that it might yet win approval.

Biden, as well as his Vice President and Democratic

presidential nominee Kamala Harris, and Republican challenger

Donald Trump, have said U.S. Steel should remain American-owned.

The company is headquartered in Pennsylvania, a hotly

contested swing state in the November presidential election.

The United Steelworkers Union vehemently opposes the deal and

both parties have sought to woo union voters.

In response to CFIUS's finding of an alleged national

security risk, Nippon Steel ( NISTF ) wrote a 100-page response letter

pledging to invest billions of dollars in U.S. Steel facilities

that otherwise would have been idled, "indisputably" allowing it

to "maintain and potentially increase domestic steelmaking

capacity in the United States."

The company also reaffirmed a promise not to transfer any

U.S. Steel production capacity or jobs outside the U.S. and said

would not interfere in any of U.S. Steel's decisions on trade

matters, including decisions to pursue trade measures under U.S.

law against unfair trade practices.