"In each of the missiles found, the presence of a chemical substance was found. It was cyclosarin," a spokesman for the Polish contingent in Iraq, Colonel Robert Strzelecki, told public television.
"They were missiles that were made 15 years ago, which should have been destroyed and were not. They would certainly have very dangerous had they fallen into the hands of terrorists," said deputy defense minister Janusz Zemke.
Washington announced on Thursday that Polish troops had discovered more than a dozen warheads containing mustard or sarin gas in Iraq, a report later confirmed by Polish Defence Minister Jerzy Szmajdzinski.
The head of Poland's military intelligence service also said on Friday that "terrorist" groups were seeking to acquire the weapons.
But a statement from the multinational forces in Iraq said on Friday that the 16 122 milimetre warheads had tested negative for chemical agents.
"Those 16 rounds were all empty and tested negative for any type of chemicals," it said.
Washington justified leading the invasion of Iraq in March 2003 by claiming the country was harbouring weapons of mass destruction. However, none has yet been found.
Poland, one of the staunchest supporters of the United States in the Iraq war, patrols a large swathe of the country south of Baghdad, heading a 6,500-strong multinational force including 2,500 Polish troops.