An inquiry opens on Tuesday into whether the UK Government misled parliament on the threat posed by Iraq, as Washington comes under fresh attack for allegedly manipulating evidence.
The threat posed by WMD was the main reason cited for war
In London, parliament's Foreign Affairs Select Committee will focus particular attention on British Government claims that Iraq had the capacity to launch a strike using weapons of mass destruction (WMDs) within 45 minutes.
Since the war was officially declared over, no such weapons have been located - although their alleged existence was a key reason cited by the US President George Bush and UK Prime Minister Tony Blair for going to war.
Watch the Foreign Affairs Committee inquiry live here at 1000 BST
In Washington, Congress is to open inquiries this week into whether the government misread or inflated threats posed by Iraq before going to war.
Such a finding is seen as having the potential to embarrass President Bush.
On Monday, a senior member of the US Senate fuelled the debate with fresh allegations.
Senator Carl Levin said he had evidence that the Central Intelligence Agency (CIA) deliberately withheld crucial information from the UN arms inspectors deployed to Iraq before the war to find evidence of banned weapons.
Mr Levin - the top Democrat on the Senate Armed Services Committee, which is reviewing the information - told reporters that if the public had known that information about alleged top weapons sites was not being shared, there would have been "greater public demand that the inspection process continue".
"Why did the CIA say that they had provided detailed information to the UN inspectors on all of the high and medium suspect sites with the UN, when they had not? Did the CIA act in this way in
order not to undermine administration policy? Was there another explanation for this?" he asked.
While Mr Levin has already made clear that he believes intelligence material may have been misused to make the case for war, the BBC's Justin Webb in Washington says this is the first time he has backed it up with one specific, and serious, allegation.
Mr Bush defended his decision to go to war in a speech on Monday.
"This nation acted to a threat from the dictator of Iraq. Now there are some who would like to rewrite history; revisionist historians is what I like to call them," the president said.
Formal probes rejected
Two former UK cabinet ministers who resigned in connection with the war against Iraq, Robin Cook and Clare Short, are due to give evidence to the committee, whose job is to assess the role played by the Foreign Office in the affair.
Both ministers were privy to confidential briefings given to the government before the war began.
Ms Short has already said she believes the prime minister had "duped" the UK into joining the war, while Mr Cook has highlighted the coalition's failure to locate chemical or biological weapons in Iraq.
This nation acted to a threat from the dictator of Iraq. Now there are some who would like to rewrite history
Both the prime minister and his director of communications, Alastair Campbell, have refused to appear before the committee, which takes evidence in public.
Downing Street has also rejected calls for a full public inquiry into its pre-war claims about Saddam Hussein's weapons capabilities.
Similarly in Washington, the Republican majority in the US Congress has rejected calls for a formal investigation, arguing that any such inquiry could harm the intelligence agencies.
The routine oversight work of the Intelligence and Armed Services committees would be enough to evaluate the Iraqi threat, Republicans say.