Five men have been arrested in Iraq and three makeshift laboratories, allegedly designed to produce sarin and mustard gas, have been uncovered.
Model helicopters, flown by remote control, were also discovered. The authorities said they would have been used to distribute chemical agents.
State television showed four hooded men in jump suits sitting alongside the haul of laboratory equipment and poisons.
Al-Qaeda's organisation in Iraq, which styles itself the "Islamic State of Iraq", is becoming steadily more effective, carrying out frequent attacks on the Shia majority and government targets. Last month, 1,045 Iraqis died violently, the highest total since 2008.
Al-Qaeda in Iraq remains the only branch of the terrorist network ever to have used chemical weapons, detonating 16 chlorine bombs in 2006 - 07. However, the gas released by these crude devices failed to kill anyone.
Mohammed al-Askari, spokesman for Iraq's defence ministry, said the latest alleged plot had wide ambitions. "There are some confessions about organised cells to smuggle chemicals outside Iraq in order to target Europe and North America," he said. "We are working with intelligence services inside and outside Iraq."
The Iraqi government's claims have not been independently verified. The country was famously found to have no chemical weapons in the aftermath of the Anglo-American invasion in 2003. How al-Qaeda would have obtained the materials to make these devices inside Iraq is unclear.