LONDON (Reuters) - The head of Britain's long-delayed official investigation into the Iraq war said on Wednesday it was impossible to predict when its report would be published, but that delays had been unavoidable due to the inquiry's complexity.
Announced in 2009, the report delving into the U.S.-led 2003 invasion of Iraq and its aftermath was expected to take a year. But last month John Chilcot, who heads the inquiry and is a former civil servant, said there was no realistic prospect of delivering conclusions before the May 7 general election.
The latest delay, to allow those criticized in the report to respond, has provoked an outcry from lawmakers and stirred up fears of a whitewash among some relatives of those killed in the war.
"The scope of this inquiry is unprecedented," Chilcot told lawmakers. "We are not concerned with a single incident and its aftermath, rather we cover decisions over a nine-year period and the consequences that flowed from them."
He said he had underestimated the amount of time it would take to analyze the evidence it had gathered, which he said had come from over 150,000 government documents and 150 witnesses.
The publication has become especially politically charged before what is expected to be a close national election. Any criticism of the opposition Labor party, which was in power at the time of the 2003 war, could damage its electoral chances.
Chilcot rejected suggestions from the parliamentary foreign affairs committee that delays in declassifying documents had been deliberate, and intended to slow the report down or keep material secret.
"It's not necessarily delay when people take time or insist on entering into a long and difficult debate ... about whether some particular point can or cannot be declassified," he said.
"I don't think I could accuse government departments of unreasonableness but substantial amounts of time were taken up at critical points."
Pressed by parliamentarians to give some indication of the report's likely publication date, Chilcot said it was "really not possible to say." But he defended the process of allowing those criticized in the report's conclusions to see the sections they were mentioned in.
Britain was Washington's main ally in the war, despite widespread public opposition to involvement in it.
Chilcot said the report had earlier been slowed down by diplomatic sensitivities about releasing exchanges between the then-U.S. and British leaders - President George W. Bush and Prime Minister Tony Blair.
Editing by Stephen Addison and Mark Heinrich