Opposition Democrats in the United States have criticised a commission set up by President Bush to investigate pre-Iraq war intelligence failures.
Bush - not Congress - chose members of the panel
House Democratic leader Nancy Pelosi said it was difficult to have confidence in a panel appointed exclusively by the president.
Others want the panel to report before the November presidential election.
The commission will also look at what the US knew about weapons programmes in North Korea, Iran and Libya.
The panel will be co-chaired by a Republican and a Democrat, and includes outspoken Republican John McCain.
Mr Bush said he wanted to know why intelligence reports about Iraq's weapons capability appeared until now to have been misleading.
The panel will "look at America's intelligence
capabilities, especially our intelligence about weapons of mass destruction", the president said in a brief statement at the White House.
The main argument used by Britain and the US for invading Iraq last March was the perceived threat from weapons of mass destruction.
But no such weapons have yet been found, despite efforts by the Iraq Survey Group formerly led by David Kay.
"We are determined to figure out why," Mr Bush said.
The commission is to submit its report by 31 March 2005 - well after the presidential election.
The BBC's Adam Brookes in Washington says that by that time, the Republicans hope that Mr Bush will be safely re-elected and largely immune to any criticism the commission might offer.
UK Prime Minister Tony Blair has also set up an independent inquiry to examine intelligence which led the country to war.
'Streak of independence'
The chairmen of the new US commission - which will be expanded to nine members - were named as former
Virginia Governor and Senator Charles Robb and retired judge Laurence Silberman.
Laurence Silberman, former judge (chair)
Senator John McCain
Chuck Robb, former Democratic senator (chair)
Lloyd Cutler, former White House counsel
Richard Levin, President Yale university
William Studeman, former CIA deputy director
Pat Wald, former US Appeals Court judge
Correspondents say the appointment of Arizona Senator John McCain will lend a streak of independence to the commission.
He has already said he believes the panel should look at the role of the politicians.
But speaking shortly after the announcement of the commission, Mr McCain told reporters: "The president of the United States, I believe, did not
manipulate any kind of information for political gain or
CIA Director George Tenet has defended the intelligence, saying the agencies had never claimed that Saddam Hussein was an "imminent threat" but warned about the future danger he could pose.
The search had to go on in Iraq for the weapons of mass destruction that US intelligence believed existed, he said.