TEHRAN, Iran — Iran said today it will enrich uranium to a higher level on its own, the latest indication the country was rejecting a U.N.-backed proposal aimed at thwarting any effort by Tehran to make material for a nuclear weapon.

President Mahmoud Ahmadinejad insisted Iran will not negotiate with the West over its nuclear program.

“You should know that even if you sizzle (from impatience or desire to talk) … the Iranian nation won’t talk to you concerning the nuclear issue,” he said.

Ahmadinejad made the comments after expressing frustration with the ongoing negotiations over the U.N. proposal that Iran exchange the bulk of its low-enriched uranium for more highly enriched fuel rods to be used in a medical research nuclear reactor.

Low-enriched uranium can be used as fuel for nuclear energy, but enriched to much higher levels, it can be used as material for a weapon. Iran currently has one operating enrichment facility that has churned out around 3,300 pounds of 3.5 percent enriched uranium over the past years, but the country needs fuel enriched to 20 percent to power a medical research reactor.

“I declare here that with the grace of God, the Iranian nation will produce 20 percent (enriched uranium) fuel and anything it needs itself,” Ahmadinejad told a cheering crowd of thousands in the central city Isfahan.

“We told them, give us the 20 percent fuel (in an exchange),” he said. “But then they started adding conditions. So we said, if you want to give us the fuel we’ll take it. If not, then fine and goodbye.”

Officials from the U.N. nuclear watchdog, the International Atomic Energy Agency, had no immediate comment.

The comments were the latest in a string of defiant statements by the Islamic Republic. On Sunday, Ahmadinejad announced Iran would build 10 more uranium enrichment facilities, despite the widespread belief that the country simply does not have the resources to match its boasts.

David Albright of the Washington-based Institute for Science and International Security, which has tracked Iran for signs of covert proliferation, said that Iran could be producing 20 percent uranium “within months” after adjusting its present enrichment program.

The real concern, said Albright, is that such a move would put Iran well on the way to making weapons grade uranium — material enriched to levels above 90 percent.

While the process of moving from the present level of enrichment to producing 20 percent enriched uranium would take months, the next stage — enriching to weapons grade — could be done “within a couple of weeks,” said Albright.

“They’re 90 percent on the way” to being able to make weapons-grade uranium “if they make 20 percent,” he said.

The idea behind the U.N.-proposed swap was to get the bulk of Iran’s uranium out of the country so it would not have enough material build a bomb and replace it with fuel rods that cannot be further enriched.

Though Iran has yet to lodge an official rejection of this proposal, the series of defiant statements over the past few days have sent a clear signal that the idea is all but dead.

British Prime Minister Gordon Brown said last month that the U.N. offer has been “comprehensively rejected” by Iran.

The IAEA passed a resolution on Friday demanding Iran to cease all enrichment immediately and halt construction on a recently revealed uranium enriching facility hidden in a mountain.

Iran reacted angrily by promising to build 10 new enrichment plants and on Tuesday Ahmadinejad said he was considering decreasing cooperation with the IAEA, the world’s only eye into the secretive country’s nuclear program.

In his speech today in Isfahan, Ahmadinejad further slammed the IAEA as being a tool of the Western powers hostile to Iran.

“They (Western countries) once again showed that they are not committed to the law. They make use of international bodies as tools … the era of such childish games are over,” he said.