Sept 4 (Reuters) - U.S. Steel would close mills

and likely move its headquarters out of Pittsburgh if the $14.9

billion buyout by Nippon Steel ( NISTF ) collapses, the Wall

Street Journal reported on Wednesday citing an interview with

the company's CEO.

The steelmaker's CEO David Burritt told WSJ the nearly $3

billion Nippon had pledged to invest in U.S. Steel's older mills

was crucial to remain competitive and maintain workers' jobs.

"We wouldn't do that if the deal falls through," Burritt

told the WSJ. "I don't have the money."

The deal has come under increasing criticism from U.S.

politicians and the United Steelworkers union since it was

announced in December.

On Tuesday, Democratic presidential candidate Kamala Harris

said U.S. Steel should remain in domestic hands, while

Republican nominee Donald Trump said he would move to block the

deal if elected.

U.S. Steel and Nippon Steel ( NISTF ) have tried to assuage concerns

around the deal and have touted its benefits.

Earlier on Wednesday, Nippon said the core senior management

as well as a majority of board members at the U.S. company would

be U.S. citizens, if the deal goes ahead.

Burritt told WSJ the expanded Arkansas mill would allow the

company to close Mon Valley, its last steelmaking operation in

Pittsburgh. The company would likely look to move its

headquarters to the South too.

The deal has received all regulatory approvals from outside

the U.S. and a greenlight from U.S. Steel's shareholders. It is

now under the regulatory review process in the United States.