Republican presidential candidate Donald Trump has demanded appointment of independent special prosecutors to investigate into the alleged wrongdoings of his Democratic rival Hillary Clinton during her tenure as the US secretary of state.

"The Justice Department is required to appoint an independent special prosecutor because it has proven itself to be a political arm of the White House," Trump, 70, said at an election rally in Ohio yesterday as he ramped up his attack on Clinton, 68, who is currently leading almost all major polls.

Trump alleged that Clinton's actions corrupted and disgraced one of the most important Departments of the government, indeed one of only four established by the US Constitution. "The Clintons' made the State Department into the same kind of Pay-to-Play operations as the Arkansas Government was: pay the Clinton Foundation huge sums of money and throw in some big speaking fees for Bill Clinton and you got to play with the State Department.

"The amounts involved, the favors done and the significant numbers of times it was done require an expedited investigation by a Special Prosecutor. After the FBI and Department of Justice whitewash of the Clinton email crimes, they certainly cannot be trusted to quickly or impartially investigate Hillary Clinton's crimes," he said.

Some former prosecutors have even suggested that the coordination between the pay-for-play State Department and the corrupt Clinton Foundation constitute a clear example of a RICO (Racketeer Influenced Corrupt Organisation) enterprise, Trump claimed.

He alleged that as the secretary of state, Clinton signed off on a deal allowing Russians to take an increased stake in a company called Uranium One, giving up control of about 20 per cent of America's uranium supply to the Russians. "Clinton's approval of the deal netted the owners of the uranium company millions of dollars. In exchange for signing off on the deal, some of the former owners of Uranium One gave the Clinton Foundation millions of dollars in donations. In addition, Bill Clinton received $500,000 for a speech to a Kremlin-backed investment firm that was a beneficiary of the deal," Trump said.