(CNN) -- The best-selling author of "Three Cups of Tea" and another book that cast light on the need to educate girls in Pakistan and Afghanistan may face a legal battle and a review from the book's publisher amid allegations that key stories in the books are false.
Greg Mortenson shot to worldwide fame with the book "Three Cups of Tea: One Man's Mission to Fight Terrorism and Build Nations ... One School at a Time," which describes his getting lost in an effort to climb K2, the world's second-highest peak, being rescued by Pakistanis in the village of Korphe and vowing to return there to build a school for local girls.
In the book, Mortenson says he was captured by the Taliban and held for several days before being released. In the sequel, "Stones into Schools," he even provides a photo of his kidnappers, 13 fierce-looking tribesmen, many of whom are clutching guns.
Among them is Mansur Khan Mahsud, who directs a Pakistani think tank specializing in research in Pakistan's remote tribal regions. (Mahsud has done research for the New America Foundation, where Peter Bergen is a director.)
Mahsud told CNN that Mortenson was not kidnapped. He said Mortenson's account of his trip to the tribal region of Waziristan, along the Afghan border, "is a pack of lies and not a single word of it is true."
He also said he plans to take legal action against the high-profile author.
"Mortenson has defamed me, my family and my tribe," Mahsud said. He said he plans to sue Mortenson, a man he once considered "a friend."
According to Mahsud, Mortenson came to South Waziristan in 1996 with one of Mahsud's relatives and stayed in the family village, Kot Langer Khel, for more than a week, where he was treated as a guest.
Rather than being kidnapped, Mahsud says, Mortenson was treated by his family as "an honored guest."
"We were his protector in South Waziristan," he said.
Mahsud provided another photo of Mortenson with his supposed kidnappers -- a picture that did not appear in the books -- in which the author is shown holding what appears to be an automatic weapon. "From his face expression you can clearly judge that this man has not been kidnapped," Mahsud said.
Mahsud claims Mortenson made up lies to "sell his book."
Mortenson's publisher, Viking, said Monday it plans to "carefully review the materials with the author" following questions first raised about the book in a CBS "60 Minutes" report that aired Sunday night.
Jon Krakauer, best-selling author of "Into Thin Air," was featured on the CBS report, saying Mortenson's account is "a beautiful story, and it's a lie."
Krakauer is a climber and former donor to Mortenson's charity. He says he was a longtime Mortenson backer, donating $75,000 to his cause, but withdrew his support over concerns the charity was being mismanaged.
A key story in "Three Cups of Tea" -- and the genesis of Mortenson's plan to build schools in the region -- is the author's tale of stumbling into the village of Korphe after his failed attempt to climb K2, where he says the villagers befriended him and nursed him back to health.
He has said he found children there forced to do their school lessons in the dirt, so he made a promise to help build a school.
"Little did I know it would change my life forever," Mortenson said of the experience in one of his speeches.
Krakauer, however, told CBS News investigator Steve Kroft in the Sunday broadcast that a "close friend" of Mortenson's who hiked back with him from K2 says Mortenson never heard of Korphe until a year after the failed climbing attempt.
In a transcript of Mortenson's written responses to questions posed to him by CBS -- a transcript posted on the website of Mortenson's charitable organization, the Central Asia Institute -- the author denies the claim is false.
He says he did visit Korphe in 1993 but that the local people "have a completely different notion about time" than those in the West, implying they would not have been able to recount the exact year he visited.
Mortenson repeats that assertion in an article posted Monday on the website for Outside magazine, a publication for outdoor enthusiasts. He admits, however, that his promise to build a school came during a second trip that happened a year later, not a few days later, as described in his best-seller.
The author chalks up some of the discrepancies to "literary license," saying co-author David Oliver Relin felt it best to compress several similar events into one "in order to be convenient" and keep it all to one book.
"So, rather than me going two or three times to one place (in the book), he would synthesize it into one trip," Mortenson told Outside. "I would squawk about it and be told that it would all work out."
There are also questions about the veracity of other episodes in the book, including Mortenson's supposed 1996 kidnapping in Waziristan in which the author describes being kidnapped by Waziri tribesmen and detained in a makeshift prison by Kalashnikov-toting guards for eight days, at which point he was suddenly released.
Krakauer calls that account "outright fiction" in an investigative report he penned about Mortenson's claims. The report was released online Monday on byliner.com.
Mortenson tells Outside that the "whole story is pretty much accurate." He says he was detained and his passport and money were taken away, but that he didn't try to escape.
After six days, he told the magazine, he explained his wife was seven months pregnant, so the men drove him to a bus station from where he could leave.
On his website, gregmortenson.com, Mortenson claims the kidnapping was carried out by the Taliban. However, the Taliban had no presence in Waziristan in 1996, arriving in the region only after their fall from power in Afghanistan in the winter of 2001.
The Taliban had also banned photography at the time that they had supposedly kidnapped Mortenson.
Mortenson expresses doubts about his own Taliban claim in the Outside magazine interview.
"As to whether they were Taliban or not? All I know is that I was in the area where the Taliban had originated," he says. "They didn't call themselves 'Taliban,' and maybe they were and maybe they weren't. But I was definitely detained against my will."
In an email sent Sunday to supporters, Mortenson says the "60 Minutes" interview "paints a distorted picture using inaccurate information, innuendo, and a microscopic focus on one year's (2009) IRS 990 financial, and a few points in the book 'Three Cups of Tea' that occurred almost 18 years ago."
Mortenson also issued a rejection of the "60 Minutes" allegations in a statement issued Friday by the Central Asia Institute, in advance of the broadcast.
Mortenson declined CBS' requests for an interview. He says in the email that he declined to appear on camera with CBS "after they attempted an eleventh-hour aggressive approach to reach me" and he decided they had a "disrespectful approach" that would result in an unfair and imbalanced report.
"The '60 Minutes' program may appear to ask simple questions, but the answers are often complex, not easily encapsulated in 10-second soundbites," Mortenson writes.
CNN has also not been able to reach Mortenson. His institute also said in a statement to CNN on Sunday that he is not commenting in person because of a medical condition.
The author also canceled two book events scheduled for this week, in Los Angeles and Honolulu.
"Greg has been suffering from hypoxia (low oxygen condition) for about 20 months, even though he still works nonstop. Last Friday, he was diagnosed with a tear hole in his heart wall that causes significant blood shunting, and he will have a heart surgical procedure done on Thursday to correct it. Once his cardiologist allows he will be able to comment on his story in person," the statement said.
Mortenson's record of charity and his tales of derring-do have helped fuel the Central Asia Institute. The organization recorded income of $14 million in 2009, the vast majority of which was raised from private individuals, many of them who were no doubt inspired by Mortenson's books.
However, in 2009, less than half of that money -- 41 percent -- actually went to building schools in Afghanistan and Pakistan, according to the institute's board of directors. On its website, the institute said "a significant portion of the remainder" was dedicated to the charity's other programs, such as outreach and education about the need for the schools.
The institute also says $1.7 million went to promote Mortenson's books in the form of advertising, events, film and professional fees, and some travel. It said the contributions generated by Mortenson's promotional events "far exceed the travel expenses."
Julie Bergman spent 12 years at the charity, including six as its chairwoman, before retiring and she remains chairwoman emeritus. She told CNN that while she cannot vouch for the credibility of Mortenson's story about Korphe in 1993, she stands by him.
"I am proud of the work we've done and Mortenson's track record," she said. "I have been to Pakistan six times to work on charity-related projects. ... I know every school and how the money was spent over 12 years."
"Into Thin Air" author Krakauer, however, said he has concerns about the finances of Mortenson's organization.
"Mortenson started with noble intentions and a great idea," Krakauer says in his investigative report. "He has built dozens of schools that have educated thousands of kids in Pakistan and Afghanistan. He deserves credit for that.
"But very soon after he launched CAI, he lost his moral bearings. He betrayed the trust of countless people, including myself. I'd like to support CAI again someday, when it's under different leadership. That part of the world needs all the effective help it can get. But with Mortenson running things, the organization went badly off the rails."
In his email Sunday to supporters, Mortenson says he recently returned from Afghanistan, where his organization plans to establish and build more than 60 schools this year.
He also says he is scheduled for surgery this week to fix the hole in his heart, and "after a few weeks my doctor says I will be as good as new."
"Three Cups of Tea" stayed on The New York Times bestseller list for four years after it was first published in 2006, becoming a global publishing sensation that has sold more than 3 million copies and been translated into 47 languages.
Three years later, in 2009, Mortenson penned the sequel "Stones into Schools: Promoting Peace with Books, not Bombs, in Afghanistan and Pakistan," which was another Times bestseller.
CNN's Maria Ebrahimji and Stan Wilson contributed to this report.