Iyad al-Samarrai of the Iraqi Islamic Party said on Thursday that the report, drafted by the chief US weapons inspector in Iraq, Charles Duelfer, proves the war was "not legitimate".
"All the information available before the war showed that [president] Saddam Hussein had put an end to his [weapons] programme," he said.
"These weapons were used as a pretext by the US and British governments to invade Iraq."
He added: "We have the right to demand compensation and the withdrawal of the occupation forces."
Suha Said, a member of the Iraqi interim parliament, said "now that the WMD file is closed, it's only natural that Washington should compensate the Iraqi people for all the damage inflicted since April 9, 2003".
The WMD report could hurt Bush
in the upcoming US elections
"The United States should now pull their troops out of Iraq and present a formal apology to the Iraqi people," she added.
The US report found that Iraq's nuclear capability, far from being reconstituted as the US had insisted before the war, was "decaying rather than being preserved" and would have taken years to rebuild.
In the build-up to the March 2003 invasion, US President George Bush had called Iraq a "gathering threat". The leaked report on Wednesday said Iraq was actually a diminishing threat.
A British report by Lord Robin Butler released in July had already charged that Prime Minister Tony Blair had taken his country to war on "very thin" grounds.
Former UN weapons inspector in Iraq Hans Blix had also condemned the war, arguing that Saddam's Iraq was never proven to possess WMD.
The report reaches the same conclusion and explains that Iraq had given up its weapons programme after the 1991 Gulf War and had not revived it when the invasion was launched in March 2003.
"This report adds nothing new," said Jassim Muhammad Salem, an editorialist for al-Mada daily.
"We have the right to demand compensation and the withdrawal of the occupation forces"
Iraqi Islamic Party
"The invasion was not motivated by the weapons of mass
destruction. Even [US President George] Bush and [Defence Secretary Donald] Rumsfeld admitted they wanted to start implementing their plan for a Greater Middle East," he said.
He was referring to a plan touted by Bush's administration as a solution to reform and democratise the Middle East but has been perceived by many as an aggressive imperialist bid.
Interim parliament member Abbas al-Bayati said the new report could also undermine Bush's credibility and benefit his Democrat rival in the 2 November presidential elections.