VIENNA, Austria - Iran told a black market supplier it was interested in "tens of thousands" of parts for its covert nuclear program, diplomats said Thursday, as the U.N. atomic watchdog prepared to rebuke Tehran for hindering an agency probe of its activities.

The diplomats, who spoke to the Associated Press on condition of anonymity, said the revelation about Iran's offer was made at a closed-door meeting of the International Atomic Energy Agency.

An IAEA report leaked last week mentioned that Iran had acknowledged inquiring about 4,000 magnets needed for uranium enrichment equipment with a European black-market supplier and had dangled the possibility of buying a "higher number" of such markets.

At Thursday's preparatory meeting for Monday's IAEA board of governors' conference an IAEA official was more precise, saying that Iran had said it was interested in "tens of thousands" of such magnets in future contracts, according to diplomats present at the closed meeting.

With two magnets per uranium enrichment centrifuge, tens of thousands of such parts would translated into a centrifuge program that significantly exceeds what Iran insists was only an experimental project.

Uranium enrichment can be used to generate power or make nuclear weapons, depending on the level of enrichment. Iran insists it was interested only in energy generation and that its offer was purposely exaggerated to spark interest from the potential black market supplier.

The United States and other nations say such arguments are an attempt to cover up nearly two decades of covert activities aimed at making nuclear weapons and point to what they say is continued Iranian secrecy on the scope of its enrichment program and other activities.

The other main area of concern remains the source of traces of weapons-grade uranium on Iranian centrifuges. Tehran asserts the traces were inadvertently imported on purchases through the nuclear black market and that it has not enriched uranium beyond the low levels used for power generation.

But IAEA investigators have not been able to test that claim because Pakistan - the main source of the equipment - has blocked free access to its nuclear material, meaning the agency cannot match isotope samples to the traces found in Iran. At Thursday's meeting Thursday, IAEA officials complained that the agency has in some cases waited in vain for information on enrichment since October.

Coming out of the meeting, Iran's chief delegate to the IAEA, Amir Zamaninia said his country had attempted to clarify "a number of misunderstandings on the part of … mainly the United States."

But another delegate present said members of the Iranian and U.S. delegations had clashed on a number of issues at what was supposed to be a technical meeting, likening their deep differences on the nature of Iran's nuclear program to a chasm between "two worlds."

The testiness reflected tensions ahead of Monday's board meeting, which is expected to censure Iran for continued foot-dragging a year into the IAEA probe of its nuclear ambitions.

A draft resolution written by France, Germany and Britain is heavily peppered with negative terms, "deploring" omissions and delays by Iran in cooperating with the agency probe or noting them with "serious concern."

Diplomats said the United States, Iran's harshest critic, was generally satisfied with the tone of the draft. But they said Washington would push for some kind of deadline for Tehran to come up with the missing information needed to prove or disprove the Islamic Republic's weapons ambitions.

Speaking in Tehran for Iran's powerful conservatives, lawmaker Manouchechr Mottaki warned of a "strong reaction" if the IAEA rules against the country at the board meeting. That meeting will review the IAEA report on Iran.