The United States will become bogged down in a quagmire if it carries out a "crazy act" against Iran, top hardline cleric Ahmad Khatami said on Friday as he blasted Washington's new nuclear policy.

Khatami, known for his anti-US vitriol, said in a Friday prayers sermon at Tehran university that Iran's friends will strike back at American interests if it is attacked.

"We have heard these threats over and over, but rest assured: if they go ahead with a crazy act, then they will be trapped in a quagmire they won't be able to get out of," he said.

"Dealing with Iran is playing with the lion's tail... if the US wants to act crazily, then friends of the Islamic revolution will endanger America's interests."

Washington, which has never ruled out launching a military strike against Iran aimed at thwarting its controversial atomic programme, on Tuesday unveiled a new nuclear policy limiting its nuclear arsenal.

It said it would use atomic weapons only in "extreme circumstances" and would not attack non-nuclear states.

However, the policy suggested that exceptions could be made for "outliers" such as Iran and North Korea, both accused by the West of flouting UN resolutions concerning their nuclear programmes.

In recent weeks, Washington has also boosted global efforts to impose new sanctions against Tehran amid suspicions that its uranium enrichment programme masks a weapons drive.

Khatami on Friday insisted that Iran only wanted nuclear technology and that a weapons programme was against its religious beliefs.

"We are not scared by the enemies' fuss. We seek only our right, and with God's help we are standing firm," he said.

Khatami, who is also a senior member of the Assembly of Experts which supervises Iran's supreme leader, said the United States has failed to hurt Iran for the past 31 years.

"You were unable to do a damn thing, and you won't be able to do anything. This nation will punch aggressors in the mouth to teach others a lesson."

The United States and Iran have had no diplomatic ties since the 1979 Islamic revolution. Animosity between them has worsened under the presidency of Mahmoud Ahmadinejad, who has refused to abandon Tehran's nuclear ambitions.