An EU internal paper has admitted that Iran will one day have enough enriched uranium to make a nuclear bomb.
Iran says it wants nuclear power, not nuclear weapons
The paper also says UN pressure has not helped to slow down Iran's nuclear programme, and that economic sanctions alone will not resolve the problem.
It was written by staff of EU foreign policy chief Javier Solana and given to EU foreign ministers on Monday.
A source said the EU was committed to a twin-track approach of UN sanctions and efforts to engage Iran in dialogue.
The source within Mr Solana's secretariat said the paper did not talk anywhere about military options, nor did it take for granted that Iran's future possession of a nuclear bomb was an "irreversible reality".
Carrot and stick
It was written to steer the foreign ministers' discussion and raised questions rather than stating answers, the source said.
The paper was leaked to the Financial Times, which quoted excerpts on Tuesday.
"At some stage we must expect that Iran will acquire the capacity to enrich uranium on the scale required for a weapons programme," the Financial Times quotes the paper as saying.
"In practice... the Iranians have pursued their programme at their own pace, the limiting factor being technical difficulties rather than resolutions by the UN or the International Atomic Energy Agency.
"The problems with Iran will not be resolved through economic sanctions alone."
The BBC's Oana Lungescu in Brussels says the paper shows the EU is looking for ways to strengthen its carrot and stick approach to Iran.
Iran says its nuclear programme is purely for civilian use.
Mr Solana and German Foreign Minister Frank-Walter Steinmeier restored tentative contacts with Iran's nuclear negotiator Ali Larijani at a security conference in Munich on Sunday.
Mr Steinmeier said after the EU foreign ministers' meeting on Monday that both of them had the impression "that in Iran there is a new ambition to return to the negotiating table".
"In the course of the next few days, we will have to sound out whether they (Iran) can pursue that line," Mr Steinmeier said.
However, Mr Solana warned: "The possibilities are not immense."