Band Of Brothers: One of 25 books by Ambrose
On Thursday the Forbes.com website reported Professor Ambrose's 1999 railway book Nothing Like It In The World contained a number of passages similar to parts of David Lavender's The Great Persuader - another book about railways.
Professor Ambrose has not commented on the claims but Victoria Meyer, a spokeswoman for The Wild Blue's publisher Simon & Schuster, said that the company's policy was to amend any errors.
"We see it as a matter of methodology, not wrongdoing," said the spokeswoman.
'Mistakes'
"There was no intent to pass off the work of another author as his own."
While apologising through his publisher for the "mistakes" of The Wild Blue, Professor Ambrose has also defended his methods, saying that he used footnotes and acknowledgments - and even praised source material.
"If I am writing up a passage and it is a story I want to tell and this story fits and a part of it is from other people's writing, I just type it up that way and put in a footnote," the author told The New York Times last week.
But many historians consider footnotes inadequate credit for passages that closely resemble those from another text.
And the renewed suggestion of plagiarism is likely to bring other works by the prolific author under scrutiny.
One of the passages from Professor Ambrose's Nothing Like It In The World quoted by Forbes.com runs as follows:
"At the end of the trip, all were appalled by Panama City. It rained continually. Mud, mildew and fungus oozed everywhere.
"Sanitation in the tent city was lacking or completely absent. Unwashed raw fruit caused epidemics of dysentery."
A passage from David Lavender's book - published in 1970 - runs similarly:
"All contemporary accounts of the beach at Panama agree it was appalling. Rain poured. Mud, mildew, and fungus oozed over everything.
"Sanitation in the improvised tent city was inadequate. Unwashed raw fruit caused epidemics of dysentery."
Allegations
Ambrose, a professor emeritus at the University of New Orleans, is the author of more than 25 books, including Band of Brothers which was made into a TV miniseries by Steven Spielberg and Tom Hanks.
The renewed allegations could be damaging for the historian's reputation, as some academics believe that no student would be allowed to borrow passages without more obvious crediting of sources.
"That's what we tell students: It's not OK, and it's equally serious when a famous author does it," said Arnita Jones, executive director of the American Historical Association.