The West must prove its claims that Iran seeks to build nuclear weapons, President Mahmoud Ahmadinejad said Wednesday, repeating his denial and insisting that it's not up to Tehran to disprove the allegations.

His remarks follow the latest report by the U.N. nuclear watchdog that cited evidence indicating that Iran is conducting secret experiments toward development of nuclear weapons.

"They (West) tells us, you should prove you don't have atomic bombs. How can something that doesn't exist be proved? It's nonexistent. How can we prove it?" he told thousands of people in Pakdasht, 25 miles southeast of the capital Tehran.

"The one who levels the accusations must prove (their) claims. You must prove that someone is guilty," he said.

Ahmadinejad said if Iran decides to build nuclear weapons, it will do so openly.

"When we say we don't possess and we don't want nuclear weapons, we mean it. But you should know that if one day the Iranian nation decides to build atomic bomb, it doesn't fear you. It will bravely stand up and say it wants to build atomic bombs," he said in his speech which was broadcast live on state TV.

Ahmadinejad said the United States, which itself has stored 5,000 nuclear weapons, charges that Iran is guilty without providing evidence, yet it wants Iran to prove its innocence.

The president also warned that Iran would treat any country that freezes its assets as a "thief."

He was reacting to reports that the U.S. and its allies might freeze assets belonging to Iran's central bank following a new set of sanctions imposed on Tehran by U.S., Canada and Britain. The new sanctions seek to apply greater pressure to get Tehran to halt its suspected nuclear weapons program.

The measures were built on previous sanctions to target Iran's oil and petrochemical industries and companies involved in nuclear procurement or enrichment activity.

"Let me tell you (West) that the slightest appropriation of the Iranian nation's currency reserves will be tantamount to theft. The Iranian nation will deal with the perpetrator as a thief," Ahmadinejad warned.