Officials from three EU powers are holding last-ditch talks with Iran on the crisis over its nuclear programme.
Western powers suspect Iran's nuclear ambitions are not peaceful
Iran requested the Brussels meeting with envoys from the UK, France and Germany, in the hope of averting moves to refer it to the UN Security Council.
EU3 foreign ministers will try to co-ordinate their stance at separate talks in London on Monday evening with US, Russian and Chinese counterparts.
The UN nuclear watchdog is due to hold urgent talks on the issue on Thursday.
The International Atomic Energy Agency (IAEA) will consider EU and US arguments that Iran should be referred to the Security Council for possible sanctions after Tehran restarted its nuclear programme.
They have accused Iran of aiming to produce nuclear weapons, but Tehran insists its nuclear programme is for civilian energy use only.
Washington, many European powers and also Israel distrust Iran, partly because it had kept its nuclear research secret for 18 years before it was revealed in 2002.
The meeting in Brussels involves diplomats from the three European nations and the Iranian deputy nuclear negotiator Javad Vaeidi.
A British spokesman said the diplomats would listen to what Tehran had to say but Europe's position remained unchanged - it was time for the UN Security Council to become involved.
30 Jan, Brussels: Iran meets EU3 foreign ministers
30 Jan, London: Permanent UN Security Council members plus Germany consider positions
2/3 Feb, Vienna: Emergency board meeting of IAEA. Possible referral to Security Council
16 Feb, Moscow: Russia and Iran resume talks on Russian compromise
Future date, New York: Possible meeting of Security Council
March, Vienna: Further IAEA report on Iranian compliance
Diplomats from the five permanant members of the Security Council, plus Germany, are set to meet over dinner in London, on the sidelines of an Afghan donor conference, to try to persuade Russia and China to agree to tough action.
US Secretary of State Condoleezza Rice is in London and will be attending the talks.
Moscow and Beijing have argued for Iran to be given more time, but neither has completely ruled out having the IAEA refer Iran to the UN Security Council.
Iranian officials had previously said they had nothing to fear from such a move, and that sanctions would hurt the West more than Iran.
Given the lack of international consensus on Iran, there has been talk of merely informing the Security Council about Iran's non-compliance with safeguards rather than referring its case there.
Iran has indicated this fudge would be unacceptable and it would still retaliate by stopping snap visits by international inspectors and pushing ahead with its enrichment programme.
However, Tehran has recently hinted it could be prepared to compromise on the nuclear issue.
Last week, Iran's nuclear negotiator, Ali Larijani, described as "useful" a Russian proposal to enrich uranium on its territory for use in Iran's nuclear programme.
However, sceptics say Iran has always staunchly refused to give up its right to produce nuclear fuel, and fear Iran's talks with Russia are merely a delaying tactic.