A French author and publisher have apologised after a history textbook suggested that the September 11 attacks were "no doubt orchestrated by the CIA".

A reference to the conspiracy theory was found in the work, 'Histoire du XXe siècle en fiches' ('History of the 20th century in flashcards'), by French publisher Ellipses.

An extract from page 204 describes how Al-Qaeda committed "the quadruple terrorist attack of 9/11 2001 in New York and Washington".

The book continues that "this world event - probably orchestrated by the CIA (secret services) to impose American influence on the Middle East? - touches the symbols of American power on its territory".

The Conspiracy Watch website has described the extract as "shocking".

The author, Jean-Pierre Rocher, a professor of history and geography, has expressed his wish that the sentence is deleted from the book.

A statement on the Ellipses website said: "This phrase, which echoes conspiracy theories devoid of any factual basis, should never have been used in this book".

"It does not reflect the editorial line of Ellipses or the position of its author."

'Histoire du XXe siècle en fiches' is reportedly targeted at undergraduate students and claims to present "the entire history of the 20th century" in short extracts.

In a statement to Euronews, Ellipses said they "bitterly regret having let slip from our vigilance" regarding the extract.

"Opinions may be freely expressed in our works, but under no circumstances can an inaccurate or unfounded fact be presented as objective truth."

Ellipses confirmed that a formal correction had been published in new copies of the book.

'Histoire du XXe siècle en fiches' was published in November, but the conspiracy theory was only highlighted when it found by a group of schoolteachers.

The extract was then reported to the Facebook page for Les Clionautes, an association of Professors of History and Geography in France.

Les Clionautes spokesperson Bruno Modica told Le Monde that the sentence was "unacceptable".