U.S. Senator Joe Lieberman, a member of the Senate Armed Services Committee, told Israel's Jerusalem Post the United States probably could not destroy Iran's nuclear program but could attempt to set it back by strikes as a last resort.

"I think the only justifiable use of military power would be an attempt to deter the development of their nuclear program if we felt there was no other way to do it," he said.

Iranian President Mahmoud Ahmadinejad, speaking at an annual military parade, said the army was ready to defend the nation.

"It will cut off the hands of any aggressors and will make any aggressor regret it," Ahmadinejad declared.

Iran says it will not drop its right to enrich uranium for peaceful use but that it will work with the IAEA.

The U.N. nuclear watchdog says it has been unable to verify that Iran's nuclear program is purely civilian but has found no hard proof of efforts to build atomic weapons.

IAEA inspectors are due in Iran on Friday to visit nuclear sites, including one at Natanz where Iran says it has enriched uranium to 3.5 percent, the level used in nuclear power plants.

IRNA news agency said Olli Heinonen, ElBaradei's deputy for safeguards issues, would lead the team. One diplomat said his presence suggested Iran might provide some missing information.

Experts say it would take Iran years to produce enough highly enriched uranium for one bomb from its current 164 centrifuges. But Iran says it will to install 3,000 centrifuges, which could make enough material for a warhead in one year.