Mr Kay cast doubt on Iraq's weapons programmes

David Kay gave no reason for leaving but sources in Washington speak of a mixture of personal reasons and his disillusionment with the search.

He did say he believed Iraq had not had any large stockpiles of chemical or biological weapons during the 1990s.

"I don't think they existed," he told Reuters news agency in an interview.

The Iraq Survey Group (ISG) team leader was appointed by the CIA last June to head the post-invasion search for chemical, nuclear and biological weapons.

The BBC's Jon Leyne in Washington says Mr Kay's words about non-existent stockpiles are powerful remarks from someone who once strongly believed Iraq's weapons of mass destruction (WDM) represented a major threat.

Mr Kay is being succeeded by former United Nations weapons inspector Charles Duelfer who said earlier this month that he believed the chances of finding chemical or biological weapons in Iraq was now "close to nil".

'Model' inspector

Announcing Mr Kay's departure, CIA director George Tenet praised him for "extraordinary service under dangerous and difficult circumstances".

"At a time when our WMD hunt efforts were just beginning, David provided a critical strategic framework," Mr Tenet said.

Mr Duelfer is known to be more of a sceptic on Iraq's weapons

He described Mr Kay as a "model private citizen who willingly lent his unique expertise to his government in a time of need".

In a statement released by the CIA, Mr Kay said he retained confidence in the ISG's continuing efforts to resolve questions about the ousted Iraqi regime's WMD efforts.

But in his telephone interview with Reuters, he cast doubt on reports that Saddam Hussein - who used chemical weapons against Kurds and in the war with Iran in the 1980s - had continued his programmes in recent years.

"What everyone was talking about is stockpiles produced after the end of the last Gulf War and I don't think there was a large-scale production programme in the 90s," he said.

Mr Kay said he believed most of what was going to be found in the hunt had already been discovered.

WMD 'activities'

In his State of the Union speech this week, President George W Bush quoted the conclusion of Mr Kay's interim report, which said only that WMD-related programme activities had been found in Iraq.

Charles Duelfer, 51, served as deputy executive chairman of the UN Special Commission on Iraq from 1993 to 2000.

He is currently leading scientists checking out suspicious finds by the US military.

Experts say he has significant connections, including relationships with Iraqis and members of the ISG.

The BBC's Matt Frei
"Kay led a team of 1,400 inspectors"