Six major world powers have agreed a package combining incentives and penalties to try to induce Iran to curb its nuclear programme.
Iran may be offered help with its civilian nuclear programme
UK Foreign Secretary Margaret Beckett said the international community was willing to resume talks with Iran if it halted sensitive nuclear activities.
Ms Beckett said action would be taken in the United Nations Security Council if Iran did not comply.
The move follows a US offer to join in talks if Iran halted enrichment.
The next step in this process will be a face-to-face meeting between the Europeans and the Iranians where the agreed package will be presented.
It is hoped the meeting will be held in the next few days.
Tehran has maintained that its nuclear activities are aimed at energy production, but the Western allies suspect it of trying to build a nuclear weapon.
Talks between Iran and European powers have been suspended since Iran resumed uranium enrichment.
'Basis for discussion'
Speaking on behalf of the US, UK, France, Germany, Russia and China, Ms Beckett said there were now two paths ahead for Iran.
"I am pleased to say that we have agreed a set of far-reaching proposals as a basis for discussion with Iran," she said.
"We urge Iran to take the positive path and to consider seriously our substantive proposals which would bring significant benefits to Iran."
She said action in the UN Security Council would be halted if Iran complied but would go ahead if it did not.
No details of the proposal will be released until Iran is briefed on the proposal, she said.
However, it is thought it may offer help with Iran's civilian nuclear programme and guaranteed supplies of reactor fuel, as well as various trade advantages and security guarantees.
Correspondents at the talks say the recent diplomatic initiatives have been carefully stage-managed and the six foreign ministers presented a united front.
The intention was to set out a very clear choice for Iran, they say, but it is not clear how tough Russia and China will allow the Western powers to be.
Major policy change
The US said on Wednesday it would join EU states in talks if Iran halted sensitive nuclear activity, but Iran responded that it would talk only if it was allowed to continue uranium enrichment.
Analysts say the US move was a major policy change and an attempt to regain the initiative in the Iran nuclear issue.
Mr Mottaki ruled out any compromise on enrichment
Both Russia and China have so far opposed UN sanctions against Iran.
But analysts say the US may have done a deal with these countries behind the scenes - that if Iran rejects the US offer of talks, Moscow and Beijing will then support a tough new UN Security Council resolution.
The BBC's Frances Harrison in Tehran says it looks as if Iran has been waiting to see what comes out of the Vienna meeting before deciding what path to take.
On Wednesday, US Secretary of State Condoleezza Rice said the US would come to the table when Iran fully and verifiably suspended its enrichment and reprocessing activities.
Iranian Foreign Minister Manouchehr Mottaki welcomed the idea of talks with the US but ruled out any compromise on enrichment.
Washington broke off diplomatic ties with Iran in 1979 and the two sides have had little official contact since.
Iran has frequently spoken of its willingness to negotiate with any country except Israel about its nuclear programme. But Washington has previously refused to countenance such talks.
The Bush administration has been under growing pressure - both from within the US and from European allies - to make an overture to Iran to break the diplomatic deadlock.