Washington, Oct 18 (IANS): The Federal Bureau of Investigation (FBI) has released some 100 pages relating to its investigation of Democratic presidential candidate Hillary Clinton's use of a private e-mail server during her tenure as Secretary of State.

Clinton, while acknowledging in hindsight that she made a mistake in bypassing the official communications channels, has insisted she did not knowingly send or receive classified information via the server, located in the basement of her home in Chappaqua, New York, EFE news reported.

One of the documents published on Monday cites an FBI agent saying that the State Department's top administrative official sought to persuade investigators to retroactively declassify a classified item found in the e-mails.

The agent, whose name was redacted, "indicated he had been contacted by Patrick Kennedy, Undersecretary of State, who had asked his assistance in altering the e-mail's classification in exchange for a 'quid pro quo'," the FBI document stated.

"In exchange for marking the e-mail unclassified, State would reciprocate by allowing the FBI to place more agents in countries where they are presently forbidden," the document said.

The e-mail in question had to do with the September 2012 attack on the US Consulate in Benghazi, Libya, which resulted in the deaths of the ambassador and three other Americans.

There was "no quid pro quo", State Department spokesman Mark Toner said on Monday when asked about the document during his daily session with reporters.

Toner added that disagreement among agencies about the proper classification of documents is common.

The FBI likewise denied any notion of a quid pro quo.

Clinton's opponent, Republican Donald Trump, was not convinced by the assurances from the State Department and the FBI, reacting to the Kennedy document with a one-word tweet: "Unbelievable".

A Trump ally, retired Lt. Gen. Michael Flynn, said the new documents "provide undeniable proof that Clinton colluded with the FBI, Department of Justice and State Department to cover up criminal activity at the highest levels."

"If any person had done a fraction of what she (Clinton) has done with our sensitive information, they would be criminally charged and those in our military would be court-martialed," the former head of the Defence Intelligence Agency said in a statement.