By Paul Reynolds
World affairs correspondent, BBC News website
The next stage in the deadlock over Iran's nuclear programme is likely to be an attempt by the United States and its allies to get the Security Council to impose more sanctions.
The latest failure in talks with Iran came in a session in London on Friday between Iran's chief negotiator Saeed Jalili and the EU's foreign policy representative, Javier Solana.
It was no surprise afterwards when Mr Solana said he was "disappointed" and Mr Jalili said that abandoning uranium enrichment was "unacceptable".
The suspension of enrichment to allow for talks about Iran's nuclear power needs is the Security Council's main demand.
There have been two rounds of sanctions. The first banned the transfer to Iran of technology and materials that could contribute to Iran's enrichment and other nuclear work.
The second prevented dealings with 28 named people and organisations, mainly connected with the Revolutionary Guard.
New sanctions could be targeted at Iran's oil industry and at trade credits for exports to Iran.
However, the unity of the Security Council is wearing thin and neither Russia nor China have shown much enthusiasm for taking sanctions significantly further.
In theory, both countries are committed to a third round.
In September, together with the US, the UK, France and Germany, they said that unless Mr Solana and a parallel report on Iran from the International Atomic Energy Agency (IAEA) had a "positive outcome", they would "finalise a text" for a third sanctions resolution.
The United States already imposes wide-ranging sanctions of its own.
If new UN sanctions are not agreed or are minimal, the EU might also initiate its own measures.
The IAEA report, earlier in November, was mixed.
It reported progress on clearing up some questions about Iran's past nuclear activities but also reported that Iran was continuing to enrich uranium and had installed nearly 3,000 centrifuges for this work.
Iran says that it intends to make nuclear power not a nuclear bomb.
The IAEA also reported that Iran had failed to stop construction of a heavy water reactor, as required by the council. Nor has it implemented a more intrusive inspection system to which it had earlier agreed.
The further question beyond sanctions is whether the US will seriously consider an attack on Iran's nuclear facilities and/or other targets - mainly the Revolutionary Guards.
Israel is getting increasingly restless about the failure of sanctions to effect a change of direction by Iran and is likely to press Washington for action at some stage.
However, the US appears reluctant at present to commit itself and Admiral William Fallon, the head of US Central Command, said the other day that a strike on Iran was not "in the offing".