The document indicated that al Qaeda members discussed as early as 2010 a plan to derail trains in the United States by placing obstructions on tracks over bridges and in valleys, a law enforcement official told CNN in 2011. No specific rail system was identified, according to the source.
Authorities believe the suspects received "direction and guidance" from elements of al Qaeda in Iran, said James Malizia, assistant commissioner for the Royal Canadian Mounted Police.
There's no evidence that the Iranian government was involved, he said.
Iran denies that al Qaeda has any presence within its borders.
Iranian Foreign Minister Ali Akbar Salehi told the country's state-run IRNA news agency that the allegation is "the most ridiculous thing" he has ever heard.