(CNN) -- As controversy continued to swirl over its financial affairs, the Central Asia Institute denied Wednesday that fundamental stories in the bestselling book that spawned the charity are not true.
The Montana-based charity also explained that Greg Mortenson, its executive director and the co-author of "Three Cups of Tea," has been hospitalized for heart surgery and "is not currently available for interviews, but he intends to respond publicly and widely as soon as he is able to do so."
Mortenson shot to worldwide fame with "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-tallest mountain, being rescued by Pakistanis in the village of Korphe and vowing to return there to build a school for local girls.
The riveting story led to the creation of the CAI, an organization that works to improve girls' education in Pakistan and Afghanistan.
In recent days, however, both Mortenson and the charity have found themselves on the defensive against accusations of mismanagement and exaggeration, if not outright fabrication, of key episodes in the 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.
In a statement issued Wednesday, the CAI defended the veracity of Mortenson's account.
"Media allegations that Greg did not visit Korphe in 1993 are false," the statement said. Mortenson "first visited Korphe in September 1993 after failing to reach the summit of K2 and he later built a school there. And Greg was, in fact, captured and held against his will in 1996, with his passport and money confiscated, although his captors did treat him well, as he accurately describes in his book."
On Tuesday, Montana Attorney General Steve Bullock said his office is looking into the CAI.
"In recent days, concerns have been raised about the management and financial affairs of the Central Asia Institute. I've been in contact with attorneys for the Institute and they have pledged their full cooperation in addressing our concerns," the attorney general said in a statement.
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 actually went to building schools in Afghanistan and Pakistan, and $1.7 million went to promote Mortenson's books, according to the institute's board of directors.
The Montana attorney general on Tuesday said his office "will not jump to any conclusions -- but we have a responsibility to make sure charitable assets are used for their intended purposes."
"Three Cups of Tea," co-written with David Oliver Relin, has become a huge international publishing phenomenon since it was published five years ago, spawning a sequel, two children's editions and translations in 19 countries.
CNN's Anna Rhett Miller contributed to this report.