Russian President Vladimir Putin has welcomed the fall of Saddam Hussein but questioned the validity of the coalition's war aim of rooting out weapons of mass destruction.
The "non-nyet-nein" alliance is seeking a new role
"If in the last moment of [the Iraqi regime's] existence it did not use them, it means they do not exist," he said after a trilateral meeting in the Russian city of St Petersburg with fellow anti-war leaders of Germany and France.
All three stressed the importance of a primary role for the UN in the reconstruction of Iraq when war ends.
Commentators say that, crushed by their failed attempt to block war in Iraq, the leaders are trying to stake a claim in the peace.
Russia's efforts to secure a peaceful outcome to the crisis were underlined on Friday by the disclosure that Yevgeni Primakov, the former Russian prime minister and Middle East envoy, was sent to Baghdad three days before war began in an attempt to secure the resignation of Saddam Hussein.
At a news conference after the talks, Mr Putin called the overthrow of Saddam Hussein "a plus".
"But the human losses, the humanitarian catastrophe, the destruction are all negatives," he said.
He said that the war itself had proved the fallacy of the original case for invasion - ridding Iraq of weapons of mass destruction.
"Even in the most acute moment of the fight for its survival, the Iraqi regime did not use such means..." he said.
"That raises the question of the expediency of the whole action."
The talks were supposed to include UN Secretary-General Kofi Annan - but he pulled out at the last minute.
There has been some suggestion he would not want to be aligned on one side of the damaging split within the UN.
French President Jacques Chirac summed up concerns stated by all three that the UN should play a central role in the reconstruction of Iraq.
Kofi Annan: was invited to St Petersburg, but decided against it
"The task of restoring the political, economic and social system of Iraq is enormous," he said. "Only the United Nations has the legitimacy to do that."
He wanted a "multi-polar... well balanced world", Mr Chirac said - touching on a fear that Mr Putin elaborated upon when he warned of the perils of undermining sovereign nations and diplomacy in the "export of capitalist, democratic revolution".
"If we allow ourselves to do that, the world will end up on a slippery slope toward an endless series of military conflicts. We cannot allow that to happen," Mr Putin said.
But Washington has already shrugged off pressures to give the UN a central place in Iraq.
On Thursday, Secretary of State Colin Powell said coalition members - who had "invested this political capital and life and treasure into this enterprise" - would play the leading role in shaping Iraq's future.
On the same day, Deputy Defense Secretary Paul Wolfowitz put it more flatly: "The UN can't be in charge".
Our correspondent, Steve Rosenberg, says the trilateral talks are a bid to regain political capital and clout lost in the damaging clash over how to deal with Iraq.
Russia, in particular, is trying to promote itself as a peacemaker, he says - not the image depicted in the headline of one of Russia's national newspapers on Friday, which dubbed the meeting "summit of the losers".