The ballroom that Donald Trump has begun building at the White House will cost up to $600 million, half of which will come from public funds contrary to what he has claimed, the Washington Post reported Tuesday.

A summary of the project, prepared for the Republican administration by the entrepreneur and of which the newspaper obtained a copy, estimated the project at $600 million in early March, half of which would be borne by the American taxpayer.

Documents from Clark Construction "show that internal cost estimates were significantly higher than what administration officials have acknowledged in their public statements or court filings," the Post reports.

"They also show that, from the moment the project was announced, it was planned to rely heavily on taxpayers' money."

The project, one of the most ambitious undertaken at this famous site in over a century, has continued to grow in scope. Its projected budget, funded primarily by private donations, had already increased from $200 million to $400 million.

Donald Trump had described it last January as a "GIFT to the United States" and has not ceased to defend it publicly.

When questioned by the newspaper, the White House simply reiterated that the funding would come from "President Trump and generous American patriots (...) to the tune of approximately $400 million."

The contractor, for its part, replied that the details were confidential and referred the questions to the administration.

The hall is being challenged in court by the National Trust for Historic Preservation (NTHP), a non-profit organization mandated by Congress for the preservation of historic buildings.

And since the attack at the press gala attended by Donald Trump in late April at a Washington hotel, the government has invoked "national security" imperatives to obtain the removal of obstacles to its construction.

The Republican president had already sparked a wave of protests by bulldozing an entire wing of the White House, for a room intended to accommodate up to 1,000 people for receptions and dinners.