Extract from the book by Pierre de Villemarest Facts & Chronicles Denied to the Public, Vol. 1:

Despite our clarification on Radio-Courtoisie (broadcast by Commander Guillaume and our Newsletter of the 15 October 2002), Le Monde did it again, attributing 5,000 deaths in March 1988 to gases spread by the Iraqis! This misinformation came from the diplomat Peter Galbraith, who had been invited by the Iranians to visit Halabja, scene of the crime. At the time, the person in charge of the CIA was Stephen Pelletiere, who nowadays deals with problems of national security at the United States Military School. However, Pelletiere describes this hawking about of such an untruth as being “an insult to intelligence”. He confirms that only the Iranians had the type of gas used at Halabja, on the Iraqi-Iranian border. The examination of the bodies of the victims showed that as they died their skin had turned blue, proof that the gas used carried a “blood agent” (without doubt cyanogen chloride or hydrogen cyanide) which Baghdad did not possess.
In fact, helped by the Iranians armed units of the Kurdish Jala Talabani had operated at Halabja. The Iraqis had used mustard gas against them. As soon as the Talabani men retreated, the Iranians had mounted a counter-attack with their gas based on cyanide, which had affected the Kurds living in that area.
Pelletiere has prepared detailed reports which can be consulted on the internet at:
http://www.fas.org/man/dod-101/ops/war/docs/3203/appb.pdf