The threat came the day after world powers referred the crisis over Iran's disputed nuclear drive back to the Security Council - which could impose sanctions - after Iran failed to respond to demands it suspend work that could lead to the production of nuclear weapons.
"Up to now the Iranian people have acted within the framework of the NPT (Non-Proliferation Treaty) and the IAEA (International Atomic Energy Agency)," the president said.
"But if they reach the conclusion that Western countries do not have goodwill and sincerity... they (the Iranian people) will revise their policy," he said in comments on the website of Iranian state television.
Iran says it only wants to enrich uranium to make reactor fuel, and rejects accusations that it wants to acquire the capacity to make weapons.
Five members lose patience
On Wednesday the five permanent members of the UN Security Council plus Germany decided they had lost patience with Iran.
"The Iranians must understand that they can't wait us out and can't hope to split a coalition - and so the first step is to go to the United Nations and speak with as common a voice as possible," US President George W. Bush said.
Iran had been offered trade, diplomatic and technology incentives as well as multilateral talks -- involving the United States - if it agreed to a suspension.
"We said, 'reasonable period of time,' 'weeks, not months.' That's what we explained to the Iranians," Mr Bush said. "They evidently didn't believe us. And so now we're going to go to the Security Council, and we're united in doing that."
The US ambassador to the UN, John Bolton, said he hoped the Security Council would be able to take action "early next week" on a draft resolution that would make a halt to Iran's uranium enrichment mandatory.
A senior US official also said that China and Russia had agreed on the steps to be taken, but added the specific sanctions had not yet been decided on.
But Mr Ahmadinejad told the world powers to "be patient and not disturb the current climate" and insisted Iran was still studying the offer.
He said Iran would give a reply at the end of Mordad, the Iranian month that ends on August 22.
The president also rejected accusations that Iran's hardline leadership was trying to buy time and exploit international divisions, but in yet another signal the country was unwilling to freeze enrichment, he repeated that Iran would not renounce it’s “absolute right to use peaceful nuclear technology".
Meanwhile Iran's top nuclear negotiator Ali Larijani insisted he remained willing to discuss the nuclear issue, but he repeated Iran would not accept an enrichment freeze as a precondition to talks.