US Secretary of State Condoleezza Rice has denied reports of a US-European compromise to grant Iran the right to continue a limited nuclear programme.
Iran faces the threat of sanctions if it does not halt its nuclear plans
"There is no US-European proposal to the Iranians. I want to say that categorically," Ms Rice told reporters.
Unnamed diplomats said the deal would allow Iran to convert uranium into gas - which it has done since August - with enrichment being carried out in Russia.
Iran has not reacted. The UN nuclear chief said a solution was close.
A spokesman for Mohammed ElBaradei, the director of the International Atomic Energy Agency (IAEA), said on Thursday: "He hopes that in the coming days the international community will be able to coalesce around a solution that is acceptable to all parties, including Iran."
And the UK - one of three European powers involved in talks on behalf of the EU - has not entirely ruled out the idea.
The Foreign Office said it was still only being discussed informally and that the technical complications would need detailed international consideration.
The flurry of discussions comes as both sides want to look flexible ahead of a crucial meeting on the issue in two weeks' time in Vienna, says the BBC's diplomatic correspondent Bridget Kendall.
She says it is a good moment to encourage a compromise - but given the recent angry rhetoric on both sides, there is only an outside chance of agreement.
Reports of the US-EU deal came days after a secret letter from Iran to the IAEA appeared to restart the diplomatic process, conducted by the UK, Germany and France - the EU3 - on behalf of the European Union.
Talks broke down in August when Tehran resumed the processing of uranium at its plant in Isfahan.
Mohamed ElBaradei has attempted to broker a compromise deal
According to the reported compromise deal, enriching the uranium, at which point weapons-grade material could be produced, would be done in Russia, before energy was transferred back to Iran.
A Russian government spokesman, Nikolai Shingaryov, told the Agence France Presse news agency that Russia had approached Iran with the new proposal, but had received no response.
The two countries enjoy close co-operation on nuclear issues, and Russia is aiding Iran on its new nuclear reactor at Bushehr.
But the US secretary of state said reports of a US-EU compromise proposal for Tehran were untrue.
"There isn't and there won't be. We are not parties to these negotiations and we don't intend to become parties to the negotiations," Ms Rice said on her way to the Middle East.
Earlier this week, Mr ElBaradei proposed creating an international stockpile of nuclear energy to remove the need for individual states to purse so-called "dual-use" nuclear programmes.
The US, which contends that Iran aims to build an atomic weapon, has threatened to take Tehran to the United Nations Security Council.
An IAEA resolution passed in September paved the way for Iran's referral to the Security Council, but the agency has not set a date for this.
Iran maintains it is only seeking to develop a civilian nuclear programme.