The board of governors of the International Atomic Energy Agency (IAEA) meets this week in Vienna to consider a report from Mohamed ElBaradei, the director-general, on Iran's nuclear programme. The item is expected to come up on Tuesday or Wednesday.
Peter Rickwood, an IAEA spokesman, said on Saturday: "The report is presented to the board and then has to go to the Security Council."
On 4 February, the IAEA's 35-nation board had reported Iran to the Security Council, but left a month for diplomacy before the council receives ElBaradei's assessment and decides what measures, if any, to take.
Condoleezza Rice, the US secretary of state, said: "After the board report, I think the Security Council will have to have a serious discussion about what the next steps will be."
Rice said there was no need to rush to sanctions.
Diplomats in Washington and Vienna said the Security Council could adopt a "presidential declaration" calling on Tehran to heed IAEA calls to suspend uranium enrichment and co-operate with inspections.
Russia, an Iranian ally, which has a veto on the Security Council, has said it opposes sanctions.
In last-ditch talks in Vienna last Friday, Iran and EU powers Britain, France and Germany failed to strike a deal that could have blocked possible council action.
The IAEA has called on Iran to suspend uranium enrichment as a confidence-building measure and to co-operate with a three-year-old agency investigation.
But Iran last month started a 10-centrifuge research cascade at a facility in Natanz, signalling that it was pushing ahead with enrichment it says is essential to make fuel for a civilian energy programme, but which could also be used to make atom bombs.
In his report, released earlier this week, ElBaradei said Iran had failed to answer crucial questions about its nuclear programme, but stopped short of saying it was making atomic weapons.
An assessment is due from
ElBaradei, IAEA director-general
Diplomats close to the IAEA said they did not expect that there would be a resolution at next week's board meeting.
In February, the board voted 27 to three to report the matter to the Security Council.
A Western diplomat told AFP that the European troika had "decided against a resolution, after hearing from Russia, China and India that there was no support for one, even including some non-aligned members".
However, the five permanent Security Council members plus Germany, which are all on the IAEA board, may issue a statement calling on Iran to honour the agency's call for it to suspend enrichment and co-operate with investigators, the diplomat said.
Iran, meanwhile, is lobbying the Europeans and Russia for a last-minute compromise "in order to keep the issue within the IAEA", and avoid Security Council action, a diplomat said.
The compromise would allow Iran to do small-scale enrichment work for research, but agree to a two-year moratorium on full-scale enrichment, which is more of a proliferation risk.
But the Europeans said on Friday that Iran must first suspend all enrichment, including research, in order to negotiate trade and security benefits in any deal.
Russia is trying to strike a compromise in which Iran would enrich on Russian soil, so that it would not get the technology that is considered the "break-out capacity" for making atomic weapons.
This compromise may include a Russian promise to let the Iranians run a cascade of 20 centrifuges for enrichment research.
But a Western diplomat said the US and the Europeans rejected such a concession.