The International Atomic Energy Agency sent a letter to U.S. officials three weeks ago informing them of the findings. The information was also sent to the U.N. Security Council in a letter from its director, Mohamed ElBaradei, that was circulated Thursday.
The IAEA is waiting for a reply from the United States, which is leading the coalition administering Iraq, officials said.
The United States has virtually cut off information-sharing with the IAEA since invading Iraq in March 2003 on the premise that the country was hiding weapons of mass destruction.
No such weapons have been found, and arms control officials now worry the war and its chaotic aftermath may have increased chances that terrorists could get their hands on materials used for unconventional weapons or that civilians may be unknowingly exposed to radioactive materials.
According to ElBaradei's letter, satellite imagery shows "extensive removal of equipment and in some instances, removal of entire buildings," in Iraq.
In addition, "large quantities of scrap, some of it contaminated, have been transferred out of Iraq from sites" previously monitored by the IAEA.
In January, the IAEA confirmed that Iraq was the likely source of radioactive material known as .
Yellowcake, or uranium oxide, could be used to build a nuclear weapon, although it would take tons of the substance refined with sophisticated technology to harvest enough uranium for a single bomb.
The yellowcake in the shipment was natural uranium ore which probably came from a known mine in Iraq that was active before the 1991 Gulf War.
The yellowcake was uncovered Dec. 16 by Rotterdam-based scrap metal company Jewometaal, which had received it in a shipment of scrap metal from a dealer in Jordan.
A small number of Iraqi missile engines have also turned up in European ports, IAEA officials said.
"It is not clear whether the removal of these items has been the result of looting activities in the aftermath of the recent war in Iraq or as part of systematic efforts to rehabilitate some of their locations," ElBaradei wrote to the council.
The IAEA has been unable to investigate, monitor or protect Iraqi nuclear materials since the U.S. invaded the country in March 2003. The United States has refused to allow the IAEA or other U.N. weapons inspectors into the country, claiming that the coalition has taken over responsibility for illicit weapons searches.
So far those searches have come up empty-handed and the CIA's first chief weapons hunter has said he no longer believes Iraq had weapons just prior to the invasion.