Western analysts, building on what was discovered by the previous U.N. inspection regime known as UNSCOM, which lasted from 1991 to 1998, and what was strongly suspected but could not be proved, believe Iraqi President Saddam Hussein is still concealing a deadly arsenal.

One 1998 assessment by the U.S. House of Representatives task force on terrorism and unconventional warfare concluded, "Despite Baghdad's protestations, Iraq does have small but very lethal operational arsenal of weapons of mass destruction and platforms capable of delivering them."

When the UNSCOM inspectors left Iraq in 1998, they said they still did not know the full extent of Iraq's chemical and biological programs but had collected both hard and circumstantial evidence suggesting that the programs were far more advanced and wider in scope than previously believed.

Possibly the most terrifying and least known area concerns Iraqi biological warfare capabilities. After repeatedly denying the existence of such programs, Iraq was forced to admit in 1995 that it had produced anthrax, aflatoxins and botulinum toxin and that it had filled missile warheads and aerial bombs with biological agents.

Iraq said it destroyed all these agents but UNSCOM suspected it had produced and hidden large amounts of all three.

Aflatoxins, a carcinogen naturally found in many nuts and some grains, causes cancer and other diseases and may have been developed for possible use as a slow agent of genocide, perhaps for use against Iraq's Kurdish minority. Botulinum toxin is one of the most toxic substances known to man.

"There was a vast discrepancy between the amount of germ cultures the Iraqis imported and what they said they used for legitimate industrial purposes. They could have hidden enough to produce four tonnes of germ warfare agents," said Jonathan Tucker, who worked on U.N. biological weapons inspection teams in Iraq in the 1990s.

There was also some circumstantial evidence that Iraq was working to develop and weaponize smallpox. There was a natural outbreak of the disease in Iraq in 1971 and scientists could have collected and stored samples.

It is known that Iraq was experimenting with camel pox, a close relative which usually attacks animals but could also harm humans. It might have also been used for experimentation because its chemistry is very close to that of smallpox.

SMALLPOX IS 'SCARIEST UNKNOWN'

"The biggest and scariest unknown is whether Iraq has access to smallpox and whether its scientists have produced a weaponized and militarized version," said Michael Barletta of the Monterey Institute of International Studies.

An assessment from the London-based International Institute of Strategic Studies concluded, "Iraq has probably retained substantial growth media and biological weapons agent (perhaps thousands of liters of anthrax) from pre-1991 stocks. The regime is capable of resuming biological weapons agent production in weeks from existing civilian facilities. It could have produced thousands of liters of anthrax, botulinum toxin and other agents since 1998."

Rod Barton, a former Australian defense official who worked on UNSCOM biological inspections in Iraq, wrote in an analysis in 2001 that he believed Baghdad may have perfected a way of freeze drying anthrax so that it would retain its potency for many years.

In the chemical weapons field, most concern centers on VX, a deadly nerve agent where a single droplet can kill. When they were ejected from Iraq in 1998, U.N. inspectors had uncovered evidence that Baghdad had imported precursors sufficient to produce 200 tonnes of the agent.