Ignoring American suggestions, key members of the EU circulated their own recommendations to other delegates at a crucial meeting of the UN atomic energy agency on Tuesday.
The latest development contradicted earlier claims by some diplomats that the US and the Europeans were making progress in drafting a common language for an International Atomic Energy Association (IAEA) resolution that would set a deadline for Iran to dispel fears it was trying to make nuclear arms.
But the latest draft that circulated informally mirrored the one that France, Britain and Germany came up with last week and was already dismissed by the US as not tough enough.
Washington demands that Iran should grant the IAEA inspectors "complete, immediate and unrestricted access, and provide full information about past illegal nuclear activities".
It also insists Tehran "suspend immediately and fully uranium enrichment and related activities, and meet all agency demands to resolve all outstanding issues nurturing suspicions of possible weapons programme".
The IAEA chief says he has found
no smoking gun yet in Iran
Moreover, the US demands the draft should include a 31 October deadline for Iran to comply.
But the EU draft remained vague on both demands and a time frame, asking only that IAEA director general Muhammad al-Baradai submit a comprehensive report before November for evaluation by the agency's board of governors.
Al-Baradai shrugged off the idea of a deadline.
"We cannot just say there is a magic date for an end to the agency's Iran probe," he said. He also repeated that his investigation had not established whether Iran was trying to make nuclear arms, as the US asserts.
"We haven't seen any concrete proof that there is a weapons programme," he said.
Revelations of the rift were expected to prove embarrassing to Washington.
The Americans "introduced amendments that were beyond what the market would bear", said one senior western diplomat who follows the IAEA. "The European draft is right now going to have support."