It was chow time for the troops at Forward Operating Base Falcon in Baghdad, but Private Scott Beauchamp had seen something that put him off his lunch.

When the American infantryman decided to write about the incident later, he had little idea that he would be starting a literary row in Washington over a series of graphic reports that purportedly described the harsh realities of a US soldier’s life in Iraq.

Last week it was suggested that he had fabricated parts of stories he filed to The New Republic, one of Washington’s foremost political weeklies.

At least three separate investigations have been launched into allegations that a number of grotesque incidents that he recounted did not ring true and may have been invented or heavily embroidered.

In the story that sparked the row, Beauchamp described a bizarre encounter with a heavily scarred woman who sat down to lunch next to members of his platoon. “After a minute or two of eating in silence, one of my friends stabbed his spoon violently into his pile of mashed potatoes,” Beauchamp wrote. “ ‘Man, I can’t eat like this’, he said [referring to the woman].”

Beauchamp suddenly found himself making obscene remarks about the disfigured woman, until she “slammed her cup down and ran out”. He immediately felt “horrified and ashamed” at what he had said. He went on to describe other incidents when soldiers behaved with a cruelty they never displayed at home – notably a driver who liked to crush stray dogs under the wheels of his Bradley fighting vehicle.

Yet for Michael Goldfarb, online editor of The Weekly Standard, and for a number of conservative bloggers writing about the war, some of the stories did not make sense. “It was too convenient for their theme of US soldier as perpetrator,” Goldfarb said last week. “It was just all a little too neat.”

The Standard challenged The New Republic to provide independent evidence that other incidents recounted in the stories had really occurred.

The New Republic declared it was standing by its soldier diarist but Franklin Foer, its editor, said the weekly would attempt to “rereport every detail” of the stories to confirm their veracity. Journalistic fraud has been a sensitive subject at The New Republic ever since it discovered in 1998 that one of its star writers, Stephen Glass, had fabricated dozens of articles.

Beauchamp has since fallen silent: his commanders have punished him for unauthorised activities by taking away his mobile phone and e-mail privileges.

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