TEHRAN, Iran - Iran's president says the West needs to prove its claims that Tehran seeks to build nuclear weapons and that it's not up to his country to disprove the allegations.

Mahmoud Ahmadinejad's remarks come in the wake of a new report by the UN nuclear watchdog suggesting Iranian work toward developing atomic weapons.

Ahmadinejad says Iran is not pursuing nuclear weapons and that it's impossible to prove something that doesn't exist. His speech Wednesday to a group of supporters near Tehran was broadcast on state TV.

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

After the latest IAEA report, the U.S., Canada and Britain imposed new, tougher sanctions on Tehran targeting its oil and petrochemical industries and the banking system.