A team from the UN nuclear watchdog is conducting a second day of checks at Iraq's largest nuclear site, Tuwaitha.
The Americans have laid down strict limits on the team's activities
The seven men from the International Atomic Energy Agency were under close American guard as they carried out their limited assignment in the baking sun.
Their mandate is confined to checking nuclear material against IAEA inventories and securing any nuclear materials lying around, and is not related to nuclear inspection missions undertaken by the IAEA prior to the US-led invasion.
The site was heavily looted for a period during the war, and there has been particular concern about barrels which once stored low-enriched uranium, known as "yellow cake".
The barrels were emptied and sold to local people for $2 each by looters. Many used the barrels to hold drinking water or food, or to wash clothes.
The team spent three hours on Saturday at the Tuwaitha site, which is 50 kilometres (30 miles) south of Baghdad.
The visit was agreed after weeks of pleading by the IAEA, which has kept the radiological materials at the site safely under UN seal for 12 years.
However, members of the UN group - all non-Americans, with expertise ranging from nuclear physics to arms-control analysis - are not authorised to look at issues of health and safety arising from, for example, the misuse of the barrels.
US soldiers delayed sealing the site even after weeks of looting
They are there solely to verify how much of the 1.8 tonnes of "yellow cake" and 500 tonnes of natural uranium has gone missing.
In preparation for the visit, the Americans ordered villagers to sell back the barrels for $3 each. The Pentagon says it has so far received about 100 of the 3,000 missing barrels.
The IAEA team is being accompanied at all times by a US weapons body which has already conducted its own checks of the site.
It is being transported in a bus driven by a US soldier, and has not been allowed to use neutral UN vehicles.
On Sunday, a Reuters cameraman filming the Tuwaitha visit had his videotape confiscated by US soldiers, who said no media coverage was permitted.
The IAEA says it expects the visit to last for about two weeks.