The release of classified U.S. documents by Wikileaks will be the "9/11 of world diplomacy", Italy's foreign minister said, urging Italian prosecutors to investigate the website.

Foreign Minister Franco Frattini, on a trip to Qatar, said he did not know the content of the files to be released but warned they would "blow up the relationship of trust between states."

"It will be the September 11th of world diplomacy," he said, Reuters reported.