"The nuclear issue has ended from our point of view," state television quoted Ahmadinejad as telling clerics in a speech in the shrine city of Qom.
"Recently they have started a new game — by testing us — but this will result in no achievement for them except humiliation," he added.
World powers — Britain, China, France, Germany, Russia and the United States — offered Tehran a new package of technological and economic incentives on Saturday in exchange for suspending uranium enrichment activities.
It was not clear if Ahmadinejad's comments — his first on the nuclear standoff since the offer was presented on Saturday by EU foreign policy chief Javier Solana — were a direct reference to the package.
"In the nuclear issue, the bullying powers have used up all their capabilities but could not break the will of the Iranian nation," Ahmadinejad was also quoted as saying by state television.
The West fears Iran could use uranium enrichment to make an atomic bomb although Tehran insists it wants only to generate nuclear energy for peaceful purposes.
The Iranian government spokesman has already said Tehran will reject any offer demanding it suspends uranium enrichment.
The UN nuclear watchdog has been investigating Iran's nuclear drive for more than five years but has never been able to conclude whether the programme is peaceful.
Iran's ambassador to the International Atomic Energy Agency Ali Asghar Soltanieh has also ruled out any freeze on enrichment, saying: "Iran will never submit to such an illegal act."
US President George W. Bush has expressed his belief that Tehran has in reality already rejected the package but both the European Union and Iran insist it will be studied.
Foreign Minister Manouchehr Mottaki said that Iran was prepared to hold negotiations on the package and would give its answer in due course.
"We have informed the group of 5+1 countries of our readiness to negotiate over our own peaceful nuclear activities," he told reporters in Uganda, where he was attending a meeting of Islamic states.
"The package put forward by the 5+1 countries is under consideration in Tehran and we will give the response at an appropriate time," he added.
The United States, Iran's arch enemy, has backed diplomatic efforts to solve the standoff but has also never ruled out a resort to military action.
Ahmadinejad again shrugged off any such threat, saying: "Our enemies are not able to inflict any harm on the country.
"Today, the enemies are psychologically so desperate and, thanks to God, any hand that comes after Iran will be quickly cut off."
