CIA spokesman Paul Gimigliano told ABC News, "I have no reason at all to think the agency was directed to fabricate the letter or that anyone here did so. In fact, a document like that would have contradicted CIA's position on the relationship between al-Qaeda and Saddam Hussein. It doesn't make any sense. If that allegation is typical of the book, it should be re-shelved under fiction."
Suskind defended his book against the criticism from Tenet, the White House and the CIA.
"I spoke to high ranking officials in the CIA who had direct first hand knowledge of who said what to whom. Many of them keep daybooks and ledgers and notes so they can get things exactly right. They are on the record in extensive statements in the book and the book stands solidly as evidence," he told ABC News.
"It's regrettable though expected that the White House would react this way. If they reacted any other way they would have to answer questions that might have some legal consequences."
Suskind explained why his sources would come forward only now, years later.
"Many of them have been walking around with this lump in their chest for five years," he said. "Some of the sources, especially some of the off the record sources, felt that at the end of this Bush era it is imperative to be truthful about this issue - going to war under false pretenses so that we settle accounts and people understand what occurred and what the truth is. So we can get past this as a country. That is a big part of what some, I think, of the motivations were when they had the opportunity to finally speak."
ABC News' Sara Just and Luis Martinez contributed to this report.