"They (must) know that any proposal that requires a halt to our peaceful (nuclear) activities will be without any value and invalid," Ahmadinejad said on state-run television after his return from a visit to Indonesia.
European governments are seeking to build on a package of economic and political incentives offered to Iran in August last year in return for a permanent end to its uranium enrichment activities.
Iran rejected last year's offer, but the Europeans have continued to try to sweeten the proposal amid expectations that they will join the United States in urging the United Nations to take steps that could lead to sanctions if Iran refuses.
"Apparently, the gentlemen (Europe and the U.S.) are living in the era of colonialism and give no value to the standing of nations," the president said.
"We don't understand what goes in their brains," Ahmadinejad said alluding to opponents of the nuclear program.
Several countries, including the United States, accuse Iran of seeking nuclear weapons. Tehran says its aims are peaceful and that it was enriching uranium to fuel electricity-generating nuclear power plants.
"They want to offer us things they call incentives in return for renouncing our rights," he said, alluding to opponents of Tehran's nuclear program.
The United States has led calls for the U.N. Security Council to adopt a binding resolution requiring Iran to halt enrichment if Tehran doesn't accept the European proposal.
Fellow veto-wielding members of the council, Britain and France, also favor taking strong measures against Iran, while Russia and China oppose sanctions and want to focus on diplomatic means.
Alluding to the council, Ahmadinejad said "when we are not present (in the decision-making process) it will be invalid for us."