Saddam Hussein, the former Iraqi president, allowed the world to believe his country had weapons of mass destruction in an attempt to deter an Iranian invasion, an FBI file has revealed.

In 20 formal interviews and five "casual conversations" with George Piro, an FBI agent, Saddam said he considered Iran to be a bigger threat to Iraq than the US.

"Hussein believed that Iraq could not appear weak to its enemies, especially Iran," the agent wrote in June 2004.

The former leader also said that Iraq had never co-operated with al Qaeda, nor met Osama bin Laden, its leader, who he described as a "zealot".

The details were among more than 100 pages of notes written by Piro after Saddam was found hiding in a "spider-hole" on a farm near Tikrit, his home town.