One UN report forecasts widespread hunger and disease among civilians.
As the US moves closer to war with Iraq, figuring out the likely human impact there - and how to prepare for it - is proving extremely difficult.
Estimating civilian and military casualties involves too many variables to be precise: New types of US weapons, the reliability of allied military intelligence, whether and how Iraq would resist an invasion bent on ousting Saddam Hussein, the condition of Iraq's civilian infrastructure, disinformation, and propaganda on both sides.
The US military is very wary of estimating enemy casualties - before or after the fact. It wants to avoid a scenario that echoes Vietnam - when many estimations of enemy losses turned out to be inflated.
"We don't do body counts," says Army General Tommy Franks, head of US forces in the Middle East and South Asia. Moreover, the Bush administration says Iraq has a clear record of making up casualty figures and scenarios - even putting its own people in harm's way.
Despite the uncertainties, United Nations planners estimate that up to half a million people "could require treatment as a result of direct or indirect injuries" resulting from war.
In a report entitled "Likely Humanitarian Scenarios," recently made public, UN contingency planners also warned that "the outbreak of diseases in epidemic if not pandemic proportions is very likely." According to a draft of the report, the nutritional status of some 3 million people "will be dire," 3.6 million people will need emergency shelter, and 900,000 Iraqis would flee to neighboring countries - with another 2 million likely to become internal refugees.