WASHINGTON, D.C.: A federal investigation into the Federal Reserve's US$2.5 billion headquarters renovation intensified this week after prosecutors sought access to the construction site, adding to mounting pressure on Chair Jerome Powell as President Donald Trump renewed threats to remove him.

Two prosecutors and an investigator from U.S. Attorney Jeanine Pirro's office made an unannounced visit to the site early this week but were turned away by a contractor and directed to Federal Reserve lawyers, according to two people familiar with the matter. The individuals spoke on condition of anonymity because they were not authorized to discuss the ongoing investigation publicly.

The probe centers on cost overruns tied to the renovation project and Powell's testimony before lawmakers last year. The current estimated cost stands at $2.5 billion, about $600 million higher than a 2022 estimate of $1.9 billion.

Despite the visit, questions remain over the strength of the case. During a closed-door hearing last month, a senior deputy in Pirro's office acknowledged that investigators had not found evidence of a crime linked to the project.

Robert Hur, an attorney for the Federal Reserve Board of Governors, pushed back against the prosecutors' actions, warning them against bypassing court rulings. Referring to their request for a site "tour" to "check on progress," Hur wrote: "Should you wish to challenge that finding, the courts provide an avenue for you; it is not appropriate for you to try to circumvent it."

The investigation has also become entangled in a political standoff over Trump's nominee to replace Powell, former Fed governor Kevin Warsh. Senator Thom Tillis, a key Republican on the Senate Banking Committee, has said he will oppose Warsh's nomination until the probe is dropped, effectively blocking progress in a closely divided committee.

Tillis criticized the inquiry as "bogus, ill-timed, ill-informed" and said there was insufficient support in the Senate to advance Warsh's nomination through alternative means. "There really is no path," he told reporters.

The Senate Banking Committee is scheduled to hold a hearing on Warsh's nomination on April 21. Powell's term as Fed chair ends May 15, but he has said he will remain in the role until a successor is confirmed. He also holds a separate term as a Fed governor through January 2028 and could remain on the board beyond his chairmanship.

Trump has continued to back the investigation, framing it as a necessary scrutiny of government spending. "It is probably corrupt, but what it really is, is incompetent," he said. "Don't you think we have to find out what happened there?"

At the same time, the president has escalated his rhetoric toward Powell, saying he would remove him if he remains on the Fed's governing board. "Well then, I'll have to fire him, OK?" Trump said.

Legal experts note that removing a Fed chair would require cause, such as misconduct. Senator Josh Hawley said that the threshold is high, calling it "a pretty tall order."

The issue of presidential authority over the Federal Reserve is also being tested in a separate case before the Supreme Court involving Fed governor Lisa Cook, whom Trump has sought to remove. Lower courts have so far allowed Cook to remain in her role, and a final ruling is pending.

Powell has argued that the investigation is a pretext to undermine the central bank's independence, raising broader concerns about political interference in U.S. monetary policy.