Iran's foreign minister has said his country is ready to talk to the US - but insisted that it will continue with uranium enrichment.
Manouchehr Mottaki called on the US to change its behaviour
The US on Wednesday said it would join EU states in talks if Iran first halted sensitive nuclear activities.
Analysts said it was a major US policy change and an attempt to regain the initiative in the Iran nuclear issue.
The world's major powers are meeting in Vienna later to discuss a package of incentives to offer to Iran.
Tehran says its nuclear activities are aimed at energy production.
The US and Western allies suspect Iran of trying to build a nuclear weapon.
Talks between Iran and European powers have been suspended since Iran resumed uranium enrichment.
Room for manoeuvre
In comments reported on Iranian state-run television, Iranian Foreign Minister Manouchehr Mottaki said Iran "will not give up our nation's natural right [to enrichment], we will not hold talks over it. But we are ready to hold talks over mutual concerns".
He added that if the US "is interested in any change in the existing situation, it should change its behaviour and behave properly and logically".
The BBC's Frances Harrison in Tehran says it is clear that Iran is keen to hold talks with the US, but that it has always insisted on its sovereign right to produce nuclear fuel, and will not want to be seen to have been bribed into giving up those rights.
Mr Mottaki's statement is not a complete dismissal of the US offer, and leaves Tehran some room for manoeuvre, she says.
Foreign ministers from Germany and the five permanent UN Security Council members - the UK, China, France, Russia and the US - will try to finalise an offer of incentives to Iran in Vienna on Thursday.
It is thought they may offer Iran help with its civilian nuclear programme and guaranteed supplies of reactor fuel, as well as various trade advantages and security guarantees.
The package is also likely to include potential punishments if the Iranians refuse to comply.
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.
Pressure on US
On Wednesday, US Secretary of State Condoleezza Rice said "as soon as Iran fully and verifiably suspends its enrichment and reprocessing activities, the United States will come to the table".
Ms Rice urged Iran to consider the new proposals
"It's time to know whether Iran is serious about negotiation or not," she added.
When asked about the possibility of pursuing a military option against Iran, she said President George Bush "was not going to take any of his options off the table".
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.
But 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.