They say the chief US investigator, Charles Duelfer, is not planning to return to the country.
Mr Duelfer reported last year that Iraq had no stockpiles of chemical or biological weapons at the time of the US-led invasion nearly two years ago.
The existence of WMD had been the stated reason in Washington and London for going to war with Iraq.
Mr Duelfer said when he released his interim report in October that former Iraqi leader Saddam Hussein had still had the desire to restart WMD programmes.
