A new round of sanctions is due to imposed on Iran today by the UN Security Council.
Members are voting on a draft resolution that is the product of five months of talks between the US, Britain, France, Germany, China and Russia.
The four Western powers wanted much tougher sanctions over Iran’s nuclear programme, but Washington says they are still tough.
US Secretary of State Hillary Clinton said: “I think it is fair that these are the most significant sanctions that Iran has ever faced. The amount of unity that has been engendered by the international community is very significant.”
If adopted, the new sanctions will include greater surveillance of Iranian banks abroad, and action against those suspected of having links to nuclear or missile programmes.
An arms embargo against Iran will be extended and enterprises run by the military and state blacklisted. A cargo inspection regime is also being set up.
40 more companies are also due to be added to a UN blacklist of companies whose assets are being frozen.