Iran's president said Sunday that his nation's pursuit of nuclear technology was irreversible, taking a tough tone ahead of a U.N. deadline this week demanding his country suspend part of its nuclear program.

The United Nations has threatened sanctions against Iran unless it halts uranium enrichment by Thursday. Iran has said it is willing to negotiate on the issue but has rejected any immediate suspension, calling the deadline illegal.

"The great decision of the iranian nation for progress and acquiring technology is a definite decision. There is no way back from this path," Ahmadinejad said in a speech on national television after giving awards to 14 nuclear officials and scientists.

Ahmadinejad said it was the United States who should give up nuclear technology because it could not be trusted with it, since it developed and used nuclear weapons.

"Our nation does not accept the claim that science and technology is good for some and bad for others because of the possibility of the diversion (to nuclear weapons)," he said

Then he added, addressing the United States: "You diverted (technology) and built weapons that killed hundreds of thousands of people ... You have to put aside all nuclear work because you are not competent. If you were competent you would have not have built and used nuclear weapons."

Iran says its nuclear program is intended solely to generate electricity, while the United States and Europe contend it secretly aims to develop weapons. The United Nations wants Iran to suspend enrichment because the key process can produce either fuel for a reactor or material for a warhead.

Ahmadinejad insisted developing nuclear reactors was Iran's right, saying, "Our nation is united in calling for the peaceful use of nuclear energy ... there is no talk of weapons."

On Saturday, Ahmadinejad inaugurated a plant for producing heavy water, which is to be used in a reactor still being built. The West fears that once the reactor is finished, Iran will extract plutonium from its byproducts for use in building a bomb.