The UN nuclear watchdog said in an internal report that some inspections in Iran were "managed" by the Iranians, who refused to let inspectors take pictures with UN cameras or use their own electronic devices.
Last month, the Iranian delegation to the UN in Vienna circulated a paper to the 35 nations on the International Atomic Energy Agency's (IAEA) Board of Governors commenting on the IAEA's February report on inspections of Iran's nuclear sites.
In this paper, Iran said that in January 2004 it had granted IAEA inspectors "full and unrestricted access" to workshops that manufactured parts for centrifuges, which are capable of producing bomb-grade material. The inspectors were taking environmental samples to test for traces of enriched uranium.
But the IAEA said its access was not unrestricted.
"The agency's visit was 'managed' by the Iranians in the sense that the inspectors were not permitted to take pictures with IAEA cameras or use their own electronic equipment," the IAEA document, obtained by Reuters, said.
The samples were taken as part of an IAEA investigation into the origins of bomb-grade uranium found at several sites in Iran.
Tehran said that the traces came from contamination of centrifuge parts by the previous Pakistani owners. The IAEA is still trying to verify this explanation.
The United States says Iran's atomic energy programme is a front to build a nuclear weapon, a charge Tehran rejects, saying its nuclear intentions are limited to electricity generation.
The IAEA document also says there are still questions about the reason why around 1990 Iran experimented with producing polonium-210, a substance that has few civilian uses but can be used to spark a chain reaction in a nuclear bomb.
"No contemporary (ca 1990) applications for Po-210 were provided by Iran as examples of their reason for pursuing the production of this isotope," the IAEA said.
At the March IAEA board meeting, the board passed a resolution that "deplores" Iran's failure to inform the UN watchdog of its experiments with items like polonium and advanced "P2" centrifuges.
Iran said it informed the IAEA of research projects in these areas well in advance. The IAEA disagreed.
"In none of the discussions with Iran in 2003 did Iranian officials make any reference to the acquisition of drawings from a foreign source, or to any mechanical tests for P2 type centrifuges," the IAEA document said.
IAEA chief Mohamed ElBaradei said the discovery of undeclared P2 designs and components was a "setback" in the IAEA's co-operation with Iran and the main reason the board approved last month's harsh resolution on Iran.