One of the pigeons, which had some metal rings and "invisible" strings attached to it, was caught near a rose water production plant in the nearby city of Kashan in Isfahan province.

A source told the newspaper, "Early this month, a black pigeon was caught bearing a blue-coated metal ring, with invisible strings." The source gave no further description of the pigeons, nor what their fate might be.

In 2007, Iran issued a formal protest over the use of espionage by the United State to produce a key intelligence report on the country’s nuclear programme.

In fact, last year Iran reportedly arrested 14 squirrels for spying, WNN reported.

Iran’s state-sponsored news agency said at the time, "The squirrels were carrying spy gear of foreign agencies, and were stopped before they could act, thanks to the alertness of our intelligence services," WWN quoted the news agency as reporting.