UNMOVIC, the UN arms team which monitored Baghdad's weapons programmes and left on the eve of the war, said it thus could not assess the interim report from the US-led Iraq Survey Group (ISG), which was completed in October.
Controversy has raged over whether the regime of Saddam Hussein had weapons of mass destruction (WMD), cited as a main reason for the US-led war that brought down Saddam.
The administration of US President George W. Bush said the October report by the ISG confirmed its statements about Saddam's weapons programmes, even though it said no WMD had been found.
But the ISG findings were not given to UNMOVIC, which focussed on biological and chemical weapons, or to the International Atomic Energy Agency (IAEA), the UN's nuclear arms watchdog, which has repeatedly asked to see it.
"The actual report was not provided to UNMOVIC or to IAEA," said Wednesday's regular update from UNMOVIC.
"In the absence of access to the full progress report and the findings, documents, interviews and materials supporting and underlying report, the commission (UNMOVIC) is not in a position to properly assess the information provided," it said.
Even though the war has toppled Saddam, UN weapons inspectors still have a mandate to work in Iraq under both UN Security Council resolutions as well as the nuclear Non-Proliferation Treaty.
The Security Council will discuss the UNMOVIC's report on Monday.