Mr Blix said it was "amazing" Mr Straw was convinced by the cluster report
Former British Foreign Secretary Jack Straw gave some incorrect answers to the UK's Iraq war inquiry, former UN weapons inspector Hans Blix has said.
Mr Blix told the BBC he was "puzzled" by some of the evidence that Mr Straw gave to the panel.
He said that Mr Straw had been incorrect to suggest, in 2002, that UN weapons inspectors were not being allowed access to certain sites.
Mr Straw is due to be interviewed by the inquiry again later on Monday.
"I'm puzzled by some of the things Jack Straw said," Mr Blix told BBC World's Hardtalk programme.
He said that Mr Straw had stated that in 2002, according to one of their own reports, UN inspectors were not being allowed access to potential weapons sites in Iraq as required under a UN resolution.
"He did not focus at all on what I had said about the increased Iraqi co-operation," he said, explaining: "he focused upon - say - that the Iraqis are not allowing you to interview people and they are stopping you from getting to sites. That was not true," he said.
January-February: Jack Straw, Tony Blair and other senior Labour figures to appear before the panel
February: Inquiry to adjourn ahead of the general election campaign
June-July: Inquiry to resume and hear from Gordon Brown among others
Report set to be published in late 2010 or early 2011
Mr Blix added that he was perplexed by Mr Straw's interpretation of the 2002 report, which he said was merely a collection of issues which needed resolving with the Iraqis.
"I think it was an amazing statement that the report, that we sent around at that time, the so-called 'cluster report', that this would have convinced him," he said.
"That report was an analysis of what Unscom [United Nations Special Commission] before us had found, and what we in our analysis had found.
"It put the cases of unresolved issues in clusters, and lined out what Iraqis could do to help us to solve them. There was nothing sensationally new in this document."
During his January appearance before the inquiry - which is examining the background to UK involvement in the March 2003 war and its aftermath - Mr Straw said he had acted "on the basis of the best evidence available at the time" about the threat posed by Iraq.
Mr Straw said the UK insisted on a series of conditions for its backing for military action, including approval by the UN, that it must be a last resort and must be lawful.
He helped negotiate a UN resolution in November 2002 giving Saddam Hussein a "final opportunity" to meet its disarmament obligations but failed to get a second resolution which, critics say, was needed to explicitly authorise military action.
Nevertheless, Mr Straw said Saddam Hussein had clearly failed to comply with the initial resolution in terms of co-operating with inspectors and providing full disclosure of his weapons capability.