In a speech, Ahmadinejad also rejected President Barack Obama's offers of engagement, saying "three or four beautiful words" don't mean U.S. policies have changed under his administration.
"They say they have extended a hand to Iran, but the Iranian government and nation declined to welcome that," he said. "What kind of hand did you extend towards the Iranian nation? What has changed? Did you lift sanctions? Did you stop propaganda? Did you reduce the pressure?"
Mr. Obama said Thursday that six world powers dealing with Iran's nuclear program will develop a package of serious new punitive measures over its refusal to halt uranium enrichment in coming weeks.
China has not confirmed U.S. reports that it has to possible new U.N. sanctions against Iran. China has veto power in the U.N. Security Council and its support would be key to passing a resolution against Iran.
Iran's top nuclear negotiator, Saeed Jalili, is in China in the hopes of winning assurances from Beijing that it will oppose sanctions.
Three rounds of earlier United Nations sanctions have already been imposed.
The U.S. and some of its allies have accused Iran of seeking to use its civilian nuclear program as a cover to develop nuclear weapons. Iran has denied the charge, saying its nuclear program is geared towards generating electricity, not bombs.
Ahmadinejad's more defiant rhetoric comes after the Wall Street Journal reported Friday that the International Atomic Energy Agency and western intelligence agencies have been investigating how an Iranian business .
Iran's economy has suffered over the past year, and parliament approved a cut in subsidies that keep fuel prices low, a further blow to Iranians already experiencing high unemployment and inflation.
Nevertheless, Ahmadinejad said U.S. steps to pressure Iran have backfired and instead have isolated Washington in the eyes of the world.
"Don't imagine that you can stop Iran's progress," Ahmadinejad said. "The more you reveal your animosity, the more it will increase our people's motivation to double efforts for construction and progress of Iran."
The U.N. Security Council could consider new punishments on Iran, including increasing financial squeezes on the extensive holdings of Iran's Revolutionary Guard. The U.S. has also said it could seek to penalize companies that sell fuel to the oil-rich Islamic republic, which imports about 40 percent of the fuel it needs because its refineries cannot keep pace.
Iran has periodically boasted of what it says is growing self-sufficiency in technological sectors like its satellite program and other scientific work.
Seeking to demonstrate that point, Ahmadinejad's speech on Saturday was to workers at the inauguration of an industrial project in southern Iran.
He said Iran need not be bothered by the prospect of new sanctions.
"They (Americans) said they want to impose fuel sanctions. ... They don't understand that they work in our favor. They imagine we will get upset should they refuse to sell gasoline to us. ... No, we immediately tell experts to produce it," he said.
Ahmadinejad said the U.S. has failed to isolate Iran. He said the fact that Mr. Obama's was not announced beforehand for security reasons was evidence of America's own isolation.
"First, let's see who is isolated. We think those who can't show up publicly among the people and directly address them are isolated, those who fear nations. Gentlemen go to a country where they have 60,000 troops without any prior announcement. Who is isolated?" Ahmadinejad said.
The Iranian president noted that his own trip to Afghanistan was announced in advance and said he was warmly received.
"You are isolated yourself, but you are hotheaded and don't understand it," Ahmadinejad said.