A top State Department official tried to pressure the FBI to change its determination that at least one of the emails on Hillary Clinton’s private server contained classified content, prompting discussion of a possible trade to resolve the issue, two FBI employees told colleagues investigating Clinton’s use of a private server last year.

One FBI official conceded that he told the State Department employee he would “look into” changing the classification of a Clinton email if the official would lend his authority to an FBI request to increase its personnel in Iraq, according to documents released by the bureau Monday.

Another bureau official described the arrangement as a “quid pro quo” and said he believed that the State Department official, Undersecretary of State for Management Patrick F. Kennedy, was interested in “minimizing the classified nature of the Clinton emails in order to protect State interests and those of Clinton,” the documents say.

No tangible swap ever came to pass. The email was classified in accordance with the FBI’s original wishes, and the bureau was not given any additional personnel in Iraq. Both the FBI and the State Department denied that a quid pro quo ever existed.

Clinton’s use of a private email server while secretary of state has dogged the Democratic presidential nominee’s campaign and has proved to be an issue that resonates with voters. The new documents could add to perceptions among voters that Clinton is not trustworthy, and they come with the final presidential debate days away and the election in just a few weeks. The revelation of possible backroom dealing was immediately seized on by her critics.

The Post’s Matt Zapotosky explains how a State Department official tried to pressure the FBI into changing the classification of an email from Hillary Clinton’s server. (Bastien Inzaurralde/The Washington Post)

In a video statement posted to his Twitter page Monday, Republican nominee Donald Trump said: “This is very big, and frankly, it’s unbelievable. What was just found out is that the Department of Justice, the State Department, and the FBI colluded, got together, to make Hillary Clinton look less guilty, and look a lot better than she looks. This is one of the big breaking stories of our time, in my opinion. This shows corruption at the highest level, and we can’t let it happen as American citizens.”

Clinton campaign spokesman Brian Fallon said in a written statement: “It is well known that there was strong disagreement among various government agencies about the decisions to retroactively classify certain material in emails sent to Secretary Clinton. Agencies that took issue with this overclassification did so based on their own beliefs, and we were not part of these disagreements that played out inside the government.”

The FBI said in a statement that it had referred the matter to the “appropriate officials for review.” The agency did not respond to a message seeking comment on who those officials are. The official at the center of the matter — who is not named in the documents — has since retired, the bureau said.

The FBI and the Justice Department declined to bring charges against Clinton for mishandling classified information while she was secretary of state, and FBI Director James B. Comey has repeatedly and forcefully defended that decision. He also has pushed the bureau to be unusually transparent in showing the public how the probe was handled, testifying personally before Congress for hours and releasing hundreds of pages of documents.

The documents released Monday include summaries of more than three dozen interviews with technology company employees, FBI agents and Diplomatic Security officers who worked with Clinton.

The allegation of a “quid pro quo” — first reported over the weekend by Fox News and the Weekly Standard — came from an official in the FBI’s records management division, who was relaying an interaction between a colleague in the international operations division and Kennedy.

According to a summary of his interview, the international operations division had been trying to reach Kennedy on an unrelated matter for some months, and Kennedy called back wanting to talk about Clinton’s emails. Kennedy, the international operations official told investigators, said he wanted to change the classification of a Clinton email that was causing problems. The State Department was reviewing the emails for release under the Freedom of Information Act. It had submitted some emails — all of which were marked unclassified — for the FBI to review, and the FBI determined that at least one appeared to contain classified information.

Not knowing the email’s content, the international operations division official said that he would “look into the email matter if Kennedy would provide authority concerning the FBI’s request to increase its personnel in Iraq,” according to a summary of his interview. The official seems to have called his colleague in the records management division.

That official told investigators that he had been “pressured” to change the email to unclassified and that Kennedy offered his colleague in international relations a “quid pro quo.” It is unclear who first broached the purported deal. As part of his job at the State Department, Kennedy helped Clinton with her BlackBerry, though he has said he was unaware of her private server.

The international operations division official eventually called Kennedy back and told him he could not change the classification of the email, which was related to the attacks on the U.S. Consulate in Benghazi. Kennedy also was allowed to press his concerns with Michael Steinbach, who heads the FBI’s national security branch, and Steinbach was similarly unyielding.

According to the documents released Monday, Steinbach told Kennedy the bureau would not change its classification decision, but it would also not discuss the matter publicly. Within an hour of that conversation, according to the FBI documents, the Associated Press published a story in which Clinton denied having sent classified emails on her private server.

Both the FBI and the State Department disputed that their employees had engaged in a quid pro quo. The agencies, though, acknowledged that Kennedy had inquired about the classification of an email, and the FBI said that in the same conversation, a bureau official “asked the State Department official if they would address a pending, unaddressed FBI request for space for additional FBI employees assigned abroad.”

The FBI said its official was not a part of the criminal Clinton email investigation.

“The classification of the email was not changed, and it remains classified today,” the bureau said in a statement. “Although there was never a quid pro quo, these allegations were nonetheless referred to the appropriate officials for review.”

State Department deputy spokesman Mark Toner said in a statement that the allegation of a quid pro quo was “inaccurate and does not align with the facts.”

“Under Secretary Kennedy sought to understand the FBI’s process for withholding certain information from public release,” Toner said. “As has been reported, there have been discussions within the interagency on issues of classification. Classification is an art, not a science, and individuals with classification authority sometimes have different views.”

Kennedy did not immediately return an email seeking comment. In his own interview with the FBI, he disputed that he had ever tried to interfere with the Freedom of Information Act process.

The documents released Monday also contain other potentially damaging allegations.

One former Diplomatic Security agent, for example, told FBI investigators that Clinton “blatantly” disregarded State Department security protocols while she was secretary of state. The former agent alleged that Clinton would ride to foreign diplomatic functions with top aide Huma Abedin, instead of the local ambassador, which the agent said violated normal procedure and embarrassed and insulted the ambassadors.

The former agent also said that on an early 2009 trip to Jakarta, Indonesia, Clinton insisted on visiting a troubled area to promote an initiative, despite a request from Diplomatic Security that the visit be scrapped for safety concerns. The agent said Diplomatic Security officials thought the trip placed staff, security agents and even reporters in danger, all for a photo opportunity “for her election campaign.”

Rosalind S. Helderman contributed to this report.