DOCUMENTS found on Friday at a school in Sierra Leone may destroy the credibility of a best-selling book by a child soldier in the 1990s civil war.

The discovery is the latest in a series of revelations casting doubt on the story told in Ishmael Beah’s A Long Way Gone, which has sold 650,000 copies in the United States and has just come out in paperback in Britain. The book is a brilliant account of the war through the eyes of a child and has become the primary text of campaigners against using children in war.

Beah, 27, who has become a Unicef advocate, said he stood by his story. “I don’t worry about it. For me, my story is accurate and I presented it accurately and I stand by it. I’m not worried about it.”

Speaking before the emergence of the latest document, he indicated the attacks were motivated by jealousy. “If you go round waving a book in Sierra Leone and asking, ‘Who knows this person?’, somebody is going to say, ‘Of course, that’s my son or could be my brother’.”

His story began in January 1993 when his village, Mattru Jong, was attacked by rebel forces. Beah, then aged 12, escaped into the bush. He spent almost a year on the run before being handed an AK-47 by a government commander. He was 13 and for the next two years massacred his way around the country, high on various drugs.

Asked last week how many people he had killed, he said: “I’ve no idea. I really don’t know. I was in it for quite some time; each day of the war, we were fighting or there were exhibition killings. When we captured prisoners, it wasn’t like real war, where you take them to prison. We lined them up and . . . It was a way of indoctrinating new recruits.”

The new documents, obtained by Peter Wilson, a London-based correspondent of the newspaper The Australian, are academic records of Beah’s school. They show his marks for the period ending March 1993, indicating that he did not leave the school when he said he did.

They seem to confirm what Wilson had already discovered - that the attack on Mattru Jong actually took place in January 1995. Since Beah is known to have been picked up by Unicef in January 1996, he can have been on the run and/or been a soldier for only a year.

Wilson has also investigated an account in the book of a fight between boys from rival factions at a Unicef rehabilitation centre in Freetown that reportedly ended with six dead. Unicef has been unable to find evidence of such an incident. But it said it was “not aware of any discrepancies in Ishmael’s story. It is our view that even one day as a child soldier is one day too many”.

Beah said: “Whose word do they [the press] have for saying it didn’t happen? They said there was an official in government who said he didn’t want to disclose his identity. They said if this thing happened they would have known about it. Then I think to myself – Sierra Leone, do they know how many children were killed in the war? Does the government know or care about that? Of course not.”

Wilson suggests that “at every step of the way Ishmael was given incentives to exaggerate”. In Freetown a Unicef nurse encouraged him to tell his story and rewarded him with a Walkman. He won a trip to New York in 1996 with his graphic descriptions of life in the war. There he met Laura Simms, a writer he now calls his mother, who helped him to make his narratives more vivid. Finally, while he was studying at Oberlin college in Ohio, a creative-writing teacher spotted his literary gifts.

Beah is angry about the inquiries into his story. His father was killed in the fighting and he points out that reports that his father was still alive were found to be false.

“They never actually apologised for dragging me through that emotional thing . . . Every other day now, I go on The Australian’s website and they have a new instalment. This is what I think: they went and they didn’t find anything so they tried to find something else just to discredit me.”

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The Sunday Times 100 best holiday reads
• What will we be reading this summer: the booksellers predict
• Literary festivals: a survivor’s guide