Major players in the UN Security Council have warned Iran it must resume talks over its nuclear programme or face isolation.
In a statement agreed after weeks of debate, the Security Council also urged Iran to halt work on uranium enrichment. The final statement accommodated Russian and Chinese demands that it should not contain any direct threat of sanctions.
Russia has argued that any action against Iran be taken through the UN's nuclear regulator, the International Atomic Energy Agency (IAEA).
Iran says that it should be allowed to make its own nuclear fuel under IAEA inspection as permitted under the Nuclear Non-Proliferation Treaty (NPT). It says it has no intention of making nuclear weapons.
Click on the links below to read about the positions taken by key countries on the 35-member IAEA board.
When the IAEA found in a report in November 2003 that Iran had concealed a programme to enrich uranium for 18 years, the US argued that it should be reported to the Security Council at once and that sanctions should be imposed on it.
The US fears that Iran is at least trying to acquire the technology to build nuclear weapons and at worst was caught actually trying to do so. It has said that it is unacceptable for Iran to develop nuclear weapons and has not ruled out any measures, including force.
It held off from pressing its case for sanctions while three European Union countries - the UK, France and Germany - tried to negotiate a voluntary and permanent cessation of all Iranian enrichment activities, and said that if Iran agreed, it would relax some of its own bilateral sanctions and help Iran join the World Trade Organization.
However, these talks have now been suspended because Iran has resumed some enrichment work and the US now believes that the time has come to go to the Security Council.
The UK joined France and Germany in an effort to negotiate with Iran that it should not develop a fuel enrichment cycle, in order to give the rest of the world complete confidence that it was sincere in its declaration that it did not intend to make a nuclear bomb.
The EU3, as they are called, offered economic incentives and promised to guarantee fuel for the nuclear reactor Russia is building for Iran. Iran agreed to stop all enrichment work while the talks continued but when the work resumed last August, the talks were suspended.
The UK therefore supports reporting Iran to the Security Council. In the first instance this would probably be for a warning but in the final analysis the UK would probably support economic sanctions. The UK is against the use of force, saying that Iran is not like Iraq.
France has adopted a similar position to that of the UK and Germany. At first it looked as if the EU3 offered a negotiated "European" solution in contrast to the policies of the US.
However, these efforts have not led anywhere and France also concludes that Iran must be referred to the Security Council. Like the UK, it holds a veto on the council, and while it is probably even more reluctant to impose sanctions than the UK, it might do so in the end.
A recent speech by President Jacques Chirac, defending French nuclear weapons and saying they could be used to counter terrorist threats, indicates that France is adopting a hard line in defence of its own nuclear posture and does not want Iran to develop its own nuclear technology.
Germany is the third member of the EU3 and its industrial power added weight to the talks with Iran. It is the largest exporters of goods to Iran and in a good position to offer incentives and threaten sanctions. In 2004, German companies exported goods worth 3.6 billion euros ($4.43 billion) and an estimated 4 billion euros in 2005 to Iran.
Like Britain and France, Germany (which with France opposed the Iraq war) would much prefer a negotiated outcome but, like the others, it too has been disappointed by the outcome of the talks with Iran on enrichment.
It therefore supports the referral of this issue to the Security Council. It voted in September (with Britain and France) that the issue was within the council's competence.
Russia is a vital player, supplying Iran with the technology for its nuclear programme. It abstained in the September vote which declared Iran in violation of its NPT commitments for having hidden its enrichment work.
Russia has proposed enriching uranium for Iran on Russian soil, thereby removing the need for Iran to have technology which could also be used in nuclear weapon production. Iran has not accepted the Russian proposal.
Because of its economic interests, Russia may not want a confrontation with Iran and its veto on the Security Council puts it in a powerful position.
China abstained in the IAEA vote in September. No country has a veto on the IAEA but China does have one in the Security Council and therefore its position is a vital one. So far it has indicated concern over the issue but opposes sanctions.
China would be reluctant to see any UN measures that prevented access to Iran's oil and gas. It signed an agreement with Iran in 2004 to buy oil and gas over a number of years and it also agreed to help develop an Iranian oil field. China could be a major stumbling block in any attempt by the US to get sanctions imposed.
It has urged Iran to return to talks with the European Union and Russia in order to "resolve the problem through diplomatic means".
To general surprise and the anger of its own left wing, the Indian government voted against Iran in the September IAEA meeting. The Indians are now coming under pressure from the US to throw their substantial weight behind a Security Council move.
The US is saying that a nuclear co-operation agreement reached between President George W Bush and Prime Minister Manmohan Singh last year may fail in the US Congress if India does not support the US in the IAEA. Washington agreed last year to share advanced civilian nuclear technology with Delhi, lifting sanctions triggered by India's nuclear tests in 1998.
On the other hand, India is also aware of its energy interests in Iran and may not want to jeopardise those. The two countries are discussing the construction of a natural gas pipeline from Iran to India.
This is how countries voted in September 2005, when the IAEA agreed that Iran was in violation of the NPT and that it was a matter within the competence of the Security Council.
Voting for: Argentina, Australia, Belgium, Canada, Ecuador, France, Germany, Ghana, Hungary, India, Italy, Japan, Republic of Korea, Netherlands, Peru, Poland, Portugal, Singapore, Slovenia, Sweden, UK, US.
Abstaining: Algeria, Brazil, China, Mexico, Nigeria, Pakistan, Russia, South Africa, Sri Lanka, Tunisia, Vietnam.