The counter-offer may be a variation of the proposal made by Europe, the US, China and Russia or could be an entirely new package, the state-run Irna news agency quoted Manouchehr Mottaki, the Iranian foreign minister, as saying on Saturday.
"We hope that Iran's real proposal, which might come within a modified or new package, will be examined carefully by Europe," he said.
Mottaki did not elaborate on how the Iranian proposal may differ from the Western package.
"We intend to take steps towards a comprehensive understanding that considers the rights of one side, Iran, and resolves the concerns of the other side at the same time," Mottaki said.
"Iran has begun examination of the European package and it will officially response to the European side."
Talks with Egypt
Separately, Iran's top nuclear negotiator, Ali Larijani, briefed Ahmed Aboul Gheit, the Egyptian foreign minister, on Tehran's position on the proposal during talks in Cairo, a statement from the Egyptian side said. Larijani and Abul Gheit were to meet again on Sunday, it said.
The package put forward by the Big Five at the UN plus Germany aims to restart negotiations with Iran over its nuclear programme.
Solana (L) presented a Western
incentives package on Tuesday
It included some significant concessions by the US aimed at enticing Tehran to freeze enrichment.
The US would provide Iran with peaceful nuclear technology, lift some sanctions and join direct negotiations with Tehran.
The package also pulls back from demands that Iran outright scrap its enrichment programme as an initial condition for negotiations, seeking instead a suspension. However, it also contains the implicit threat of UN sanctions if Iran remains defiant.
When presented with the proposal's details on Tuesday, Iran said they contain "positive steps" but also ambiguities, which it said had to be cleared up in further talks. It said it would study the package before announcing its stance.
EU foreign policy chief Javier Solana, who presented the offer to Tehran, said he expected a reply within "weeks".
Iran has consistently refused to give up enrichment, a process that can produce either fuel for a nuclear reactor or the material for a nuclear warhead. Iran insists its programme is peaceful and that it has the right to develop enrichment - though it has signalled it might compromise on large-scale enrichment.
On Friday, a powerful hardline cleric, Ayatollah Ahmad Jannati, came out against the Western incentive package, reflecting conservative pressure on the government to reject the offer.
"It's not good for Iran," Jannati said in his Friday prayer sermon, telling worshippers that the West has "no choice but to accept" an Iranian enrichment programme.