WASHINGTON — A former CIA officer who says she spent years under deep cover has written what appears to be one of the most revealing memoirs ever put to paper by an American intelligence operative — a book so intriguing that Apple bought the television rights even before its October publication date.

But the book, "Life Undercover: Coming of Age in the CIA," by Amaryllis Fox, has become embroiled in dual controversies.

Some former CIA officers who have learned about its contents are questioning its veracity, saying key details don't ring true. Some are casting doubt on the book's climactic scene, Fox's recounting of a dramatic solo meeting she says she had in Karachi, Pakistan, with al Qaeda-linked extremists.

And, in an extraordinary move, Fox submitted her memoir to publisher Knopf Doubleday without getting approval from the CIA's Publication Review Board, in violation of the nondisclosure agreement every agency officer signs, according to three U.S. officials familiar with the matter. That agreement says the CIA must review anything a former officer writes about intelligence matters to insure that she is not revealing secrets or endangering lives.

The CIA says it must complete the review before the material is "shared with publishers, blog-subscribers, a TV audience, ghost-writers, co-authors, editors, family members, assistants, representatives, or anyone else not authorized to receive or review such classified information." (Fox has given the manuscript to the agency but has not received approval for publication.)

The CIA had no immediate comment.

Paul Bogaards, a spokesman for Knopf Doubleday, told NBC News, "Fox has written a rich and resonant work about the path one takes, and the duty one assumes, to live a life of service and honor to country."

An excerpt of the book has appeared in Vogue magazine, and a review copy has circulated widely, including to NBC News. It contains the sort of details the CIA has censored from previous memoirs.

For example, Fox writes about posing as an international art dealer while living in Shanghai and seeking to infiltrate nuclear weapons procurement networks in Europe and the Middle East. She offers details about how the CIA uses secret software — "covcom," for covert communications" — to message sources in foreign countries. She describes disguises, surveillance avoidance techniques and how the CIA obtained false identifications from motor vehicle and passport agencies.

The details are particularly sensitive because Fox says she operated under nonofficial cover, meaning she posed as a private citizen, not a diplomat. So-called NOCs put themselves at greater risk because they lack diplomatic immunity and can be arrested and jailed if caught spying. The CIA doesn't discuss how it uses NOCs. Nor does the agency typically allow officers to name countries in which they operated, other than war zones.

The cover of "Life Undercover: Coming of Age in The CIA," by Amaryllis Fox. Penguin Random House

Fox, who is now married to a grandson of Robert F. Kennedy, acknowledged to NBC News that the advance copy did not have final approval from the CIA, but she said she submitted a manuscript more than a year ago and the agency has so far requested only minor changes that she agreed to. She said she will make further changes to the final version to mollify agency censors.

"They know where to find me," she said. "They have had a copy for over a year, and they have never identified a single sentence or section they wanted to redact."

She said in a telephone interview that she changed certain facts to protect national security, including names, places and "operational details."

But she said any fictionalization was mostly inconsequential.

"My aim was really to capture the kind of 'Capital T' Truth, the emotional truth of going through this transformation," she said, speaking of her emotional journey as she came to empathize with some of the people the CIA was hunting and killing. "And that is something you can do and still maintain accuracy by not only changing names and places but by having compelling characters and situations I met along the way without identifying them directly."

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Fox said two of the characters in the book "have composite characteristics to mask their identities."

The fact that Fox's book was submitted to her publisher without the agency's approval was first reported Thursday by Yashar Ali in his newsletter.

Fox, who says she served roughly from 2002 to 2010, says her book is largely a positive portrayal of the CIA, an ode to the unsung heroes of the intelligence world.

Current and former CIA officials confirmed that Fox worked for the CIA, though all contacted by NBC News were either unfamiliar with or unwilling to discuss the details of her career.

She writes that she was recruited while a graduate student at Georgetown University after she developed an algorithm that predicted the likelihood that an area would be used as a terrorist safe haven.

She provided NBC News with a copy of her thesis, but her thesis adviser, the terrorism expert Dan Byman, told NBC News he did not recall the algorithm but did remember that Fox was a bright and capable student.

Fox says she was helped into the agency by Dallas Jones, who was then the CIA analyst in residence at Georgetown. A person familiar with Jones's account says he did help her get hired at the agency.

Fox writes that she spent a stint as an analyst at CIA headquarters before being recruited into what was then known as the National Clandestine Service, the CIA's operations arm — the division that spies overseas.

According to her book, she was sent to the agency training base in Virginia known as the Farm, where she learned how to spot surveillance, develop rapport with potential sources, and shoot an M4 rifle.

She says she was assigned to the section of the CIA's Counterterrorism Center that focuses on terrorist's pursuit of weapons of mass destruction — CTC/WMD, in agency parlance.

Fox writes that she was allowed to design her own non-official cover, and she picked the art world because her family had ties to it.

She ultimately was sent to live in Shanghai, she writes, not to spy there, but to bolster her cover as an art dealer and disassociate herself from Washington. She says she lived with her husband, Dean Fox, a CIA case officer who served in Afghanistan.

Fox writes powerfully about the stresses of living under cover, including what that life does to relationships. She married her first husband, a British subject, mainly because it was a choice between marriage and breaking up. That marriage was annulled, and her marriage to Fox didn't survive, either.

One thing that came between them, she writes, was her increasing conviction that the CIA was too quick to use lethal force against terrorists.

"I find that building trust simply works better than exerting force," she writes. "Detention simply works better than assassination."

Fox details the recruitment of a source in the illicit arms dealing world, a Hungarian named Jakab who sells nuclear precursors to terror groups. Jakab ultimately tells her about a plan to detonate a radiation bomb in Karachi, Pakistan, she writes.

In the book's climatic scene, she describes meeting in Karachi with armed extremists affiliated with al Qaeda and the Taliban in an effort to convince them to stop their compatriots from setting off the bomb. She portrays the meeting as a success, in part because she offered a Jihadi some clove oil to help with his baby daughter's asthma. She doesn't mention any security team or coordination with Pakistani intelligence.

Four former CIA case officers raised questions about that account, saying the agency would never have sent an American case officer alone to a meeting with dangerous extremists in Pakistan.

Typically, CIA operations in Pakistan during that period were conducted in coordination with Pakistani intelligence, said the officers, including one who played a key role in the same section in which Fox says she worked.

"If someone proposed an operation like that to me, I would send them back for remedial training," he said.

Even if the CIA decided to meet a source in Pakistan without telling the Pakistanis, the former officers said, it would have made no sense to send a nonofficial cover officer instead of one operating under diplomatic cover who would have a measure of legal protection if caught.

If that and other scenes in the book really happened, Fox may be revealing sensitive information, agency veterans say. And if it didn't, she may be violating one of the core tenets of nonfiction writing, says Samuel Freedman, who teaches courses in ethics and nonfiction writing as a journalism professor at Columbia University.

Freedman said any changes of fact in a nonfiction book raise questions.

"If she wants to write that kind of a book, why not do it as a work of fiction?" he said.

Fox says her book is true, even if every detail isn't.

The CIA’s right of review was affirmed by the Supreme Court in 1980 in the case of former officer Frank Snepp, whose book about the agency’s role in Vietnam did not go through agency censors.

The CIA's prepublication review process has been roundly criticized as slow and conservative, but agency veterans say they recall only one other time in recent history when a former operative totally bypassed it. In 2012, a former officer, writing under the pseudonym Ishmael Jones, published a highly critical memoir without CIA approval after he said the agency review board sought to block almost all of it.

The CIA sued him and won a judgment seizing all revenues the officer had or would derive from the book, including TV and movie rights. One of the reasons CIA leaders were so concerned with Jones' account, former officers tell NBC News, was that he described operating under nonofficial cover.

In a lesser-known case in 2013, the CIA went to court once again to seize book revenues from a contractor who published without going through the review process.

In theory, the agency could file a similar lawsuit against Fox, though doing so would call more attention to her book.

In 2016, a former CIA case officer who served in Afghanistan published a memoir, "Left of Boom," that was heavily redacted by the CIA. His description of an operation to take down a bomb-making network was rendered practically incomprehensible by blacked-out portions, which he chose to leave in the final copy.

Last year, former CIA analyst Nada Bakos sued the agency over what she viewed as unreasonable delays in the approval of her book, "The Targeter: My Life in the CIA, Hunting Terrorists and Challenging the White House."

Bakos told NBC News that as frustrated as she was, she never considered publishing without CIA approval. She negotiated a mutually agreeable set of redactions.

What Fox has done, she said, "is so irresponsible. It's not up to her to decide what is classified and what isn't."

Fox says her book reveals no secrets.

"There is nothing in here that is a surprise to anyone who follows this," she said.

"I wrote this book to share the lessons I learned in the field about peacemaking and finding common ground. Many think of CIA as adversarial and war-mongering. My experience was very different. At its best, it's an organization dedicated to the subtle and challenging art of building trust and nurturing relationships to save lives and prevent attacks."