A senior aide to Mohamed ElBaradei, head of the International Atomic Energy Agency - the UN's nuclear watchdog - sent a letter to Peter Hoekstra, Republican chairman of the House of Representatives Permanent Select Committee on Intelligence, complaining that the report included serious distortions of IAEA findings.
The letter said the errors suggested that Iran's nuclear fuel programme was much more advanced than a series of IAEA reports and Washington's own intelligence assessments had determined.
It also said the agency secretariat took "strong exception to the incorrect and misleading assertion" that the IAEA decided to remove a senior safeguards inspector for supposedly concluding that Iran intended to build nuclear weapons.
The congressional report contained "an outrageous and dishonest suggestion" the inspector was removed for having not stuck to an alleged IAEA policy barring its "officials from telling the whole truth" about Iran, said the letter.
Diplomats have said the inspector is still the IAEA's Iran section head.
The committee will decide whether to respond to the IAEA letter, he added.
A senior aide to Elbaradei wrote
the complaint to the committee
The 29-page report was written by the staff of a panel subcommittee and was never discussed or voted on by the full 21-member House Intelligence Committee.
Jane Harman of California, the panel's senior Democratic Representative, advised party colleagues in an email that the report employed "analytical shortcuts" that presented Iran as a more dire threat than it is, aides said.
Jamal Ware, House committee spokesman, admitted that the caption on a photograph of the Natanz nuclear facility said incorrectly that Iran had produced weapons-grade material, but he said, "There are no errors in the report."
Ware said report findings were based on discussions among committee staff and a variety of sources including IAEA staff members.
The IAEA has been inspecting Iran's nuclear programme since 2003.
Although it has found no hard evidence that Iran is working on atomic weapons, it has uncovered many activities linked to uranium enrichment, a process of purifying fuel for nuclear power plants or weapons.