Iran says its stance on its nuclear programme remains unchanged, despite an EU offer of incentives to suspend uranium enrichment.
A government spokesman said the country was prepared to negotiate with major world powers, but insisted the talks must address Iran's nuclear rights.
He was speaking a day after Iran formally responded to the EU offer.
Correspondents say the latest statement suggests Iran is not ready to slow down its nuclear activities.
The exact content of both the EU proposal and the Iranian response have not yet been made public.
In the first official comments since Iran submitted its response to the EU, spokesman Gholamhossein Elham said that Iran "will not go back on its rights on the nuclear issue".
"Iran's stand regarding its peaceful nuclear program has not changed. Iran insists on negotiations while respecting its rights and avoiding any loss of international rights," he said.
The BBC's John Leyne in Tehran said it is difficult to see how any talks will last if Iran is unwilling to compromise on its nuclear programme.
The incentives package from China, the EU, France, Russia, the UK and US was offered to Iran by EU foreign policy chief Javier Solana in June.
Mr Solana also asked Iran to accept a six-week freeze on further developments on its controversial programme, in return for a similar freeze on new UN sanctions.
Separately, the EU also imposed new sanctions on Iran in June.
The incentives package builds on a previous offer of 2006 and says that if Iran suspends uranium enrichment, then talks can start about a long-term agreement.
On offer is recognition of Iran's right to develop nuclear energy for peaceful purposes and the treatment of Iran in "the same manner" as other states under the Nuclear Non-Proliferation Treaty.
Iran would get help with developing nuclear power stations and be guaranteed fuel for them.
It would also be offered trade concessions, including the possible lifting of US sanctions preventing it from buying new civilian aircraft and parts.
Tehran has consistently denied Western claims that it is seeking to build a nuclear weapon, saying its programme is peaceful.
It has repeatedly rejected demands to halt enriching uranium, which can be used as fuel for power plants or material for weapons if refined to a greater degree.
Our correspondent says it may be significant that the latest tough comments came from an official close to President Ahmadinejad.
Some officials have hinted that a compromise could be possible, but the president has repeatedly restated his commitment to the nuclear programme.