The letter was among a series of memos between Saddam's office, military intelligence and the army found by United States troops in Iraq; they do not say if the attack was carried out.
The planned attack appears to have been part of the 1987-88 campaign that left more than 180,000 Kurds dead and demolished hundreds of Kurdish villages in northern Iraq. In the most notorious incident, the town of Halabja was bombed with mustard and nerve gas in 1988, killing 5,000 residents.
In the papers released by the US, a report from Iraq's military intelligence details the bases of Kurdish rebels, led by Ibrahim Barzani, and Iranian troops.
Saddam's secretary replies, saying, "The leader Mr President has ordered that your department study with experts a surprise attack with special ammunition in the areas of Barzani's gangs and the [former Iranian leader Ayatollah] Khomeini Guards."
"Special ammunition" is the phrase used throughout Saddam's regime for chemical weapons. Later documents mention specifically the nerve agent sarin and mustard gas.
The US military says the government "has made no determination regarding the authenticity of the documents, validity or factual accuracy of the information contained therein".