“America is weaker compared to 20 years ago and it does not have its previous power and grandeur,” Khamenei said in a speech at a religious conference, state television reported.
“America and its followers are stuck in a whirlpool and they sink deeper as time passes. A dangerous future is predicted for them,” he added.
The United States cut diplomatic ties with Iran in 1980 during the siege of its embassy in Tehran by Islamist students in the wake of the Islamic revolution which deposed the US-backed shah.
Relations have remained frozen ever since and are marked by continued emnity, with the United States labelled as the “Great Satan” by Tehran.
“In the eternal battle between right and wrong, the Great Satan will lose out,” added Khamenei.
Strains have increased in recent months over Iran’s controversial nuclear programme and the detention by Tehran of three US-Iranians accused of harming national security.
Although US and Iranian officials have this year met three times in landmark talks in Baghdad aimed at bringing security to Iraq they have failed to make any significant breakthrough.
Khamenei’s comments also came just days after it emerged US President George W. Bush was set to issue an executive order blacklisting Iran’s Revolutionary Guards as a terrorist group in order to block its assets.
The Guards, one of the key institutions in the Islamic republic and increasingly powerful in the economy, has brushed aside the charges as “superficial measures” and vowed that the force would not be deterred.
