Iran on Sunday rejected demands the West is reportedly to submit at talks due to take place in days, saying it will neither close its Fordo nuclear bunker nor give up higher-level uranium enrichment.
Those two demands, outlined by European and US diplomats to The New York Times newspaper, were "irrational," the head of Iran's Atomic Energy Organisation, Fereydoon Abbasi Davani, told ISNA news agency in a lengthy interview.
Fordo, an underground bunker near the holy city of Qom, "is built underground because of sanctions and the threats of attacks," he pointed out.
"If they do not threaten us and guarantee that no aggression will occur, then there would be no need for countries to build facilities underground. They should change their behaviour and language," he said.
Iran's enrichment of uranium to 20 percent purity would likewise continue, despite unease from members of the P5+1 group -- the five permanent UN Security Council members plus Germany -- that it produced uranium stock just a few steps short of military-grade 90-percent purity, Abbasi Davani said.
"We do not see any rationale for such a request from the P5+1," he said.
But, he added, "We will not produce 20 percent enrichment fuel more than what we need, because it is not in our benefit to produce and keep it."
Iran says it needs 20-percent enriched uranium to produce medical isotopes in its Tehran research reactor, and lower, 3.5-percent enriched uranium for electricity generation in its Bushehr reactor.
It insists that its entire nuclear programme is for exclusively peaceful ends.
The United States and its European allies, however, fear the higher enrichment is part of a drive to develop a nuclear weapons capability.
The New York Times quoted unnamed US and EU diplomats as saying the West would call for Fordo to be closed immediately and dismantled, and for uranium enrichment to 20 percent to be halted and for existing stockpiles to be shipped out of Iran.
The demands would be the opening move in what US President Barack Obama has called Iran's "last chance" to resolve the showdown over the nuclear issue diplomatically, the report said.
"We have no idea how the Iranians will react," the paper quoted one senior administration official as saying. "We probably won't know after the first meeting."
Israel has threatened to launch an attack if Iran is deemed to be about to enter a "zone of immunity" that would put its atomic activities beyond the reach of Israeli missiles.
The United States has said military action is a last option, and has put its energies into tightening the sanctions noose on Iran while trying to engage it diplomatically.
Talks between the P5+1 and Iran are seen as a chance to defuse tensions and find ways to overcome mutual suspicions.
But while both sides agree the planned two days of negotiations should begin on Friday, there is still no agreement on the venue.
Iran had initially proposed Istanbul -- the host of the last round of talks, which failed in January 2011 -- but then dropped it after Turkey lent backing to the opposition in its chief ally Syria, and suggested Baghdad or Beijing instead.
Iranian President Mahmoud Ahmadinejad said in a statement on his official website: Iran is ready for negotiations and welcomes any suggestion for cooperation."
He said "Iran has practical suggestions for the upcoming meeting," but did not elaborate.
Ahmadinejad stressed again that his country was not seeking atomic weapons and he noted that Iran's nuclear activities were under the supervision of the International Atomic Energy Agency.
He also underlined that the United States was promoting the interests of Israel, the Middle East's sole if undeclared nuclear weapons state.
"The parties who are against the Iranian people have very close relations with some nations who have atomic bombs, but they are constantly pressuring us on some pretext of Iran supposedly building an atomic bomb in the far future," he said.
Iran, Ahmadinejad said in a separate speech carried by his website, "will continue with force on the path it has embarked on."