Polish President Aleksander Kwasniewski says his country was misled about the alleged threat from Iraqi weapons of mass destruction.
Kwasniewski (l) has so far stood by the US over Iraq
However he also defended the decision to go to war in Iraq and said he had no plans to withdraw Polish soldiers.
Poland was a strong supporter of the US-led invasion and has the fourth-largest contingent of occupying troops.
The remarks came a week after the Madrid bombings and as public support for Poland's role in Iraq is declining.
"Of course I feel a certain discomfort that we were misled about weapons of mass destruction," Mr Kwasniewski told journalists on Thursday.
He refused to point the finger of blame at either the US or the UK, and insisted the decision to go to war had been the right one.
"Iraq today, without Saddam Hussein, is a much better place than Iraq with Saddam Hussein," the Polish president said.
Poland has been one of Washington's staunchest allies on Iraq.
Warsaw contributed combat troops to the invasion and now commands a 9,500-strong multinational force in central Iraq.
Spain - which also has troops in the area - has said it will pull them out unless sovereignty is transferred to Iraqis as planned, following the surprise election victory of the Socialist Party in last weekend's election.
Mr Kwasniewski did not say why he had chosen to make his comments now.
Other government officials told the BBC that Poland had not changed its policy on Iraq.
The country's strong support for the war caused a rift with its European partners Germany and France.
Some polls suggest public support for Poland's role in Iraq has declined to 35%.