"The Iraqis have consistently stated that they (weapons of mass destruction) were destroyed in the summer of 1991," Hans Blix told journalists in Stockholm on Tuesday.
"My guess is that there are no weapons of mass destruction left."
Blix was in Stockholm to announce the creation of a new independent international commission on weapons of mass destruction (WMD). He said there was reason to look further into Iraqi claims after the capture of former Iraqi President Saddam Hussein.
"Saddam must have knowledge about what he ordered. He should know about what he built" and "he must have some information himself on when they destroyed their weapons of mass destruction."
Blix added the capture of Saddam Hussein was unlikely to bring the occupation forces in Iraq any closer to finding the elusive weapons, but that he may still tell investigators how Iraq acquired, developed and eventually got rid of the weapons.
A former Swedish diplomat, Blix was charged with searching for weapons of mass destruction in the 15 weeks leading up to the US-led invasion of Iraq.
He criticised the US for making claims to justify its strike on Iraq that it couldn't back up.
"I think that much of what was said was not sufficiently well based," he said.
Blix has been assigned to lead a new Swedish-financed commission on weapons of mass destruction, which is set to work in 2004 and 2005 on finding ways of limiting the spread of nuclear, chemical and biological weapons.
The new commission will cover the general threat posed by weapons of mass destruction, but Blix said it would also discuss countries of particular concern, like North Korea, Iran, Iraq and the Indian peninsula, as well as the risk posed by terrorist organisations.