(Sharecast News) - The Department of Justice has dropped its probe of Federal Reserve chair Jerome Powell, clearing the way to appoint Donald Trump's nominee Kevin Warsh to take over as successor, as political pressure mounts on the US central bank to cut interest rates.

Prosecutor Jeanine Pirro said on Friday that the criminal investigation into Powell, focused on his congressional testimony about internal overspending at the Fed, has now been closed.

Powell, who was set to step down from his position on 15 May, was forced to continue working past the end of his term after the probe caused delays to the appointment of his successor. Last week, Trump threatened to fire Powell if he did not resign.

North Carolina Republican senator Thom Tillis, who is part of the Senate Banking Committee that signs off Fed nominees, has been vocal about his opposition to Warsh's nomination while the investigation into Powell was still ongoing. He has called the probe "weak and frivolous [...] and nothing more than a failed attack on Fed independence".

Powell's eight-year stint has been marred over the past year by an ongoing spat with the president, who has repeatedly called on the central bank to lower interest rates.

After Powell refused to bow to political pressure, Trump launched an investigation into the Fed chair regarding substantial cost overruns in the renovation of two buildings owned by the central bank.

Last month, judge James Boasberg ruled that the probe was unjustified, saying that Pirro had "no evidence". Powell, meanwhile, continues to claim that it was simply a tactic by the Trump administration to undermine the Fed's power as an independent agency.

Commenting on the closure of the investigation's closure on Friday, Pirro said: "I expect a comprehensive report in short order and am confident the outcome will assist in resolving, once and for all, the questions that led this office to issue subpoenas.

"Note well, however, that I will not hesitate to restart a criminal investigation should the facts warrant doing so," she said.

Democrat Elizabeth Warren, who also sits on the SBC, said the end of the probe "is just an attempt to clear the path for Senate Republicans to install President Trump's sock pocket Kevin Warsh as Fed Chair".

"Anyone who believes Donald Trump's corrupt scheme to take over the Fed is over is fooling themselves. The Senate should not proceed with the nomination of Kevin Warsh," Warren said in a statement.