Accusations the US and Israel jointly created the computer virus Flame have been printed by the Washington Post newspaper.
It quoted unnamed "Western officials with knowledge of the effort" as its sources.
The powerful malware was discovered after the UN noticed data disappearing from PCs in the Middle East.
The Post said the US National Security Agency, the CIA and Israel's military had collaborated on the project.
It had "intended to slow Iran's nuclear program, reduce the pressure for a conventional military attack and extend the timetable for diplomacy and sanctions", the newspaper said.
Reuters subsequently reported that current and former Western national security officials had told the news agency the US had been involved in making the virus.
The BBC has been unable to confirm or disprove the allegations.