A leading Republican on the House oversight committee is asking Attorney General Eric Holder why the FBI probe into former CIA Director David Petraeus apparently remains open 16 months after he resigned from the agency following an affair with his biographer.

Rep. Jason Chaffetz, R-Utah, pressed Holder on the matter in a letter, which was reviewed by Fox News -- and suggested the probe is being left open to keep Petraeus "quiet" on issues like the Benghazi terror attack.

"My understanding is that, as of today, the investigation into General Petraeus, is still ongoing. Why is the investigation still ongoing? When will the investigation conclude? What are the issues still in question?" he wrote.

In a separate interview, Chaffetz told Fox News that Holder had promised to answer a series of questions regarding the FBI investigation following a May 2013 hearing -- including on when Holder first knew about the investigation into one of the nation's most senior intelligence officials, when he notified the president, and at what point Petraeus likely knew he was under scrutiny. However, Chaffetz said he has not heard back.

"It's been nearly two years since the investigation started on General Petraeus -- if there is something serious and sinister, then let Congress know. If not, give this man's reputation back. But I worry that the White House is just holding this over his head to keep him quiet," Chaffetz said.

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Lawmakers, including the powerful head of the Senate Intelligence Committee, Democrat Dianne Feinstein, complained in the days immediately after Petraeus' resignation in November 2012 that the Justice Department failed to notify Congress of the probe.

"A decision was made somewhere not to brief us, which is atypical," Feinstein told NBC News. "This is certainly an operationally sensitive matter. But we weren't briefed. I don't know who made that decision."

During the May 2013 hearing, Holder defended the decision, stating the issues in question were not "national security" problems. Separately, three sources tell Fox News that the FBI notified Petraeus' CIA security detail in the late spring of 2012 that his schedule was compromised, based on a review of the email traffic with his biographer Paula Broadwell.

Chaffetz said the FBI investigation may remain open, nearly two years after it began, for political reasons -- and pointed to ongoing controversy over the administration's flawed public narrative about the Benghazi terror attack.

"In the context of Benghazi, General Petraeus knows a lot about what happened with those talking points, what was going on there at the CIA. But he's now in silence mode because of this investigation," Chaffetz said. "We want to get that done. I worry that the investigation is being held over his head to keep him quiet. And that isn't right."

Petraeus has not spoken formally to the media about the scandal, and most recently was in the news when a new biography of Hillary Clinton quoted the former CIA director regarding her handling of Benghazi.

"She'd make a tremendous president," Petraeus told the authors of "HRC." "Like a lot of great leaders, her most impressive qualities were most visible during tough times. ... In the wake of the Benghazi attacks, for example, she was extraordinarily resolute, determined and controlled."

Chaffetz said it is important for the Justice Department to clear up the matter, especially given recent Republican allegations against Petraeus' former No. 2 at the CIA, Michael Morell, who is accused of misleading Congress over the administration's role crafting the talking points. Republicans on the Senate Intelligence Committee said in a January 2014 Benghazi report that Morell insisted the talking points were sent to the White House for informational purposes, and not for their input -- but emails, later released by the administration, showed otherwise.

Morell, who excised half the talking points text -- to the dismay of Petraeus, according to emails released by the administration -- has taken on high-profile assignments for the Obama White House since leaving the CIA which include the NSA review panel and the President's Intelligence Advisory Board. He is now a paid TV commentator for CBS News, has a book deal, and works for Beacon Global Strategies, whose founder Philippe Reines has been described by the New York Times magazine as Hillary Clinton's "principal gatekeeper."

House Intelligence Committee Chairman Mike Rogers, R-Mich., told Fox News on Feb. 27 that Morell will likely be recalled to testify. He said he was considering whether to recall Petraeus as well.

Both the Justice Department and FBI have previously declined to discuss the status of the Petraeus case, which Fox News is told includes an investigation of whether classified information was improperly shared. In FBI Director James Comey's January 2014 roundtable with reporters, Fox News asked about the status of the Benghazi investigation.

Comey said: "I think the only update I can give you is still ... an active and enormous priority for the FBI. Something we're working very hard on. Something we've made good progress on, and I probably have to leave it cryptically there."

When questioned whether it was wise to even ask about the Petraeus case and why it was still open, given Comey's limited comments on the Benghazi investigation, Comey responded. "You shouldn't ask me about any particular case."

Fox News asked the FBI, the Justice Department and Petraeus for comment on Chaffetz' letter, but there was no immediate response.