The counteroffer may be a variation of the proposal made by Europe, the United States, China and Russia or could be an entirely new package, Manouchehr Mottaki said, according to the state-run news agency IRNA.
"We hope that Iran's real proposal, which might come within a modified or new package, will be examined carefully by Europe," he said.
He did not elaborate on how the Iranian proposal might differ from the Western package.
"We intend to take steps toward 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."
Meanwhile, Iran's top nuclear negotiator, Ali Larijani, briefed Egyptian Foreign Minister Ahmed Aboul Gheit 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 Sunday, it said.
The package put forward by the five permanent members of the U.N. Security Council plus Germany aims to restart negotiations with Iran over its nuclear program.
It included some significant concessions by Washington aimed at enticing Tehran to freeze enrichment. The United States 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 program as an initial condition for negotiations, seeking a suspension instead. However, it also contains the implicit threat of U.N. sanctions if Iran remains defiant.
When presented with the details Tuesday, Iran said the package contains "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 conveyed 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 program is peaceful and that it has the right to develop enrichment — though it has signaled it might compromise on large-scale enrichment.
On Friday, a powerful hard-line 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 program.
Jannati is the head of the powerful Guardian Council, a constitutional watchdog arbitrating between the parliament and the government. He holds considerable influence, but the ultimate power in state matters lies with supreme leader Ayatollah Ali Khamenei, who has sometimes overruled hard-liners on the nuclear issue.