U.S. presidential candidate Hillary Clinton listens to remarks at a roundtable campaign event with small businesses in Cedar Falls, Iowa, United States, May 19, 2015. REUTERS/Jim Young Though Hillary Clinton claimed to have given the State Department all emails from the private server she used during her time as Secretary of State, the agency says it has received several more emails related to Libya that Clinton reportedly failed to submit.

The trove of documents were released this week by a House panel investigating the 2012 attack in Benghazi, Libya,

The emails all predate the Sept. 11 assault on the US diplomatic facility and include scant words written by Clinton herself, the officials said.

The documents consist of more in a series of would-be intelligence reports passed to her by longtime political confidant Sidney Blumenthal, the officials said.

The New York Times reports Blumenthal turned over 15 emails to the House committee investigating the Benghazi attack — messages that were not included in the 30,000 emails Clinton gave to the State Department last year.

Then-White House adviser Sidney Blumenthal in 1998. Reuters/Mark Wilson

"She has turned over 55,000 pages of materials to the State Department, including all emails in her possession from Mr. Blumenthal," said Nick Merrill, a Clinton campaign spokesman, when asked about the discrepancy.

Confusion over the additional emails submitted by Blumenthal — who was subpoenaed for the documents by the Benghazi committee — apparently forced the committee's chairman Rep. Trey Gowdy (R-South Carolina) to question why those emails weren't included in the documents the State Department submitted on behalf of Clinton.

House Select Committee on Benghazi Chairman Trey Gowdy (R-SC) (R) and committee member Rep. Jim Jordan (R-OH) before a closed door meeting in the House Visitors Center at the U.S. Capitol June 16, 2015 in Washington, DC. Chip Somodevilla/Getty Images

The State Department responded that it could not find the Blumenthal emails among the collection of documents Clinton had given to them, the Times reports.

Clinton is running for the 2016 Democratic presidential nomination.

Her use of the non-government email while in office was kept hidden from all but a small circle of aides, outside advisers, family members and friends. She says the single account for personal and professional purposes was a matter of convenience, and says all her work emails were included in the 55,000 pages of documents she later handed over to the State Department. Emails of a personal nature were destroyed, she says.

The State Department informed the Select Benghazi Committee on Thursday that they are no longer certain that's the case, according to officials who spoke on condition of anonymity because they weren't authorized to speak publicly on the matter.

The officials said Julia Frifield, the assistant secretary of state for legislative affairs, confirmed that nine emails and parts of six others that the committee made public Monday couldn't be located in the department's records.

Sidney Blumenthal (C), a longtime Hillary Clinton friend who was an unofficial adviser while she was secretary of state, is trailed by reporters as he takes a lunch break from being deposed in private session of the House Select Committee on Benghazi at the U.S. Capitol in Washington June 16, 2015. REUTERS/Jonathan Ernst

As for 46 other, previously unreleased Libya-related Blumenthal emails published by the committee, officials said all are in the department's records.

They weren't handed over to congressional investigators because they had no relevance to events in Benghazi and did not correspond to the committee's request, the officials said. The officials added that they are willing to provide emails outside the committee's initial request, but warned that doing so would require more time.

The emails missing from the State Department's records include missives from Blumenthal in which he sends media accounts about the killing of one of Libyan dictator Moammar Gadhafi's sons, various reports on internal politics among Libya's rebels and news of the assassination of a former Gadhafi minister in Vienna.

The last email was sent Aug. 28, 2012, two weeks before the Benghazi attack, and none focus particularly on the eastern Libyan city.

U.S. Secretary of State Hillary Rodham Clinton checks her mobile phone after her address to the Security Council at United Nations headquarters, Monday, March 12, 2012. AP Clinton's responses are brief. In one from August 2011, she tells Blumenthal she will be in Paris the next day to meet rebel leaders and says she had "to resort to new iPad" because she didn't have electricity or Blackberry coverage after Hurricane Irene.

In another from March 2012, she passes on an adviser's skepticism regarding one of Blumenthal's reports about political intrigue in post-Gadhafi Libya, saying: "This strain credulity based on what I know. Any other info about it?"

And after a long August 2012 note from Blumenthal about Libya's new interim President Mohamed Yousef el-Magariaf, Clinton writes: "Another keeper — thanks and please keep 'em coming." Four days later, she responds to a follow-up reports about el-Magariaf, saying: "Fascinating. I had a very good call w him."

Clinton's critics are likely to focus less on the substance of the emails than on the fact that they weren't shared with the State Department.

Rep. Trey Gowdy (R-SC) interrogates IRS Commissioner John Koskinen as he testifies before the House Oversight and Government Reform Committee in Washington Monday June 23, 2014. REUTERS/James Lawler Duggan

Rep. Trey Gowdy of South Carolina, the Benghazi panel's Republican chairman, has pressed for an explanation of why Blumenthal gave the committee emails not previously shared by the State Department. The suggestion has been that either the department or Clinton was hiding something.

Clinton aides say her submission to the department included all emails from Blumenthal and a dozen more exchanges that weren't in the records he provided the House committee. They said some from Blumenthal's record, which was provided as a Microsoft Word document, couldn't be confirmed as having been sent as emails.

State Department officials also questioned the provenance of some exchanges because they weren't formatted as emails.