Deadline
Earlier this month US officials said they had evidence Iran was providing weapons to Iraqi Shia militias. At the time, Iranian President Mahmoud Ahmadinejad said the accusations were "excuses to prolong the stay" of US forces in Iraq.
Middle East analysts have recently voiced their fears of catastrophic consequences for any such US attack on Iran.
Britain's previous ambassador to Tehran, Sir Richard Dalton, told the BBC it would backfire badly by probably encouraging the Iranian government to develop a nuclear weapon in the long term.
Last year Iran resumed uranium enrichment - a process that can make fuel for power stations or, if greatly enriched, material for a nuclear bomb.
Tehran insists its programme is for civil use only, but Western countries suspect Iran is trying to build nuclear weapons.
The UN Security Council has called on Iran to suspend its enrichment of uranium by 21 February.
If it does not, and if the International Atomic Energy Agency confirms this, the resolution says that further economic sanctions will be considered.