Britain, Germany and France defied the United States last month by offering Iran the prospect of sharing unspecified technology if it stops its disputed nuclear programme, it has emerged.
Another condition was that Iran accepts tougher UN inspections of its fuel enrichment programme.
A joint letter by the big three European foreign ministers was delivered to Tehran in early August despite intense lobbying by Washington.
European diplomats said they were disappointed there had not been a more specific reply so far.
The trio urged Iran to sign, implement and ratify a protocol to the nuclear Non-Proliferation Treaty, mandating short-notice inspections, and to halt its uranium enrichment programme, which the West fears could be at the heart of a secret nuclear arms programme.
Despite a subsequent ultimatum by the UN nuclear watchdog to Tehran to prove by October 31st that it is has no secret atomic weapons programme, a diplomat from one of the three European states said: "The offer still stands."