French Prime Minister Jean-Pierre Raffarin, has said that the United States erred in going to war with Iraq "morally, politically and strategically".
Straight talking from France
The criticism is unusually direct compared to the normally measured terms of diplomatic exchanges between allies.
Mr Raffarin stressed that France was not anti-American but said the friendship allowed for frankness.
He was speaking on the eve of Friday's summit in Paris of the foreign ministers of France, Russia and Germany - the three countries most vocal in their opposition to the war.
We think that with this war we've gone beyond the law
"It should be said - there was an alternative to war," he declared.
France was on the side of peace and law, without being pacifist, Mr Raffarin said, "and we think that with this war we've gone beyond the law".
Mr Raffarin regretted the "extreme violence" of the war and said it was a grave political error to "make trouble" in the Middle East.
France was strongly opposed to military action without exhausting all other means of disarming Iraq, and led efforts at the UN Security Council to give the weapons inspectors more time.
The remarks by Mr Raffarin were the most direct since his foreign minister Dominique de Villepin argued the French stance to the Security Council last month - receiving rare applause.
The French foreign minister is then heading for a meeting at the Vatican with Pope John Paul and talks with the foreign minister of Italy, who backs the US decision to go to war.