The US presidential candidate, Hillary Clinton, has criticised her aides after she was accused of taking pre-arranged questions at a rally in Iowa.
The allegation was made by a student, who said a Clinton campaign aide asked her to pose a specific question.
Mrs Clinton said she had been unaware her aides had planted the question.
Question-planting has been used in US campaigns, but is usually avoided because it can become an embarrassment for candidates when revealed.
A student at Grinnell College, Muriel Gallo-Chasanoff, told her campus newspaper she had been asked by a Clinton aide to pose a question about global warming at a rally in Newton, Iowa.
"It was news to me," Mrs Clinton said, "and neither I nor my campaign approve of that, and it will certainly not be tolerated."
Planting questions is not illicit during US elections, but the allegations could affect Mrs Clinton's campaign. She has already been accused of avoiding tough questions, analysts say.
Mrs Clinton is locked in a tough battle in the Iowa caucus with her Democratic opponents Barack Obama and John Edwards, and the revelations could affect her standing in opinion polls.
She enjoys a commanding lead nationwide, but an upset in Iowa, which kick-starts the primary season on 3 January, could give fresh impetus to her main rivals.
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