US President Donald Trump said on Wednesday that he was not currently planning to fire Federal Reserve chair Jerome Powell, but added that he did not rule it out.

Trump's mixed messaging, after months of escalating attacks on the independent central bank chief, sent the yield on the 30-year US Treasury bond surging above five percent.

Asked about whether he would eject Powell, Trump said he is "doing a lousy job but no, I'm not talking about that".

"I don't rule out anything, but I think it's highly unlikely," he added.

Trump noted that he would in any case be able to make a change at the top of the Fed when Powell's term ends next year.

"We'll pick somebody that's good," Trump said. "We want to see lower interest rates."

Powell's term at the helm of the US central bank does not conclude until May 2026, and his term as a Fed governor is up at a later date.

The Fed chair has said that he did not plan to step down early, and considers the central bank's independence over monetary policy to be a matter of law.

A US Supreme Court order recently suggested that Fed officials cannot be taken out of their jobs over policy disagreements, meaning they have to be removed "for cause," which could be interpreted to mean wrongdoing. (AFP)