Iran on Monday said the US was facing a "historic" defeat as an arms embargo against Tehran is to be lifted within days despite Washington's bid to have it extended.

Addressing the issue at a news conference, foreign ministry spokesman Saeed Khatibzadeh also lashed out at the "insanity" of the latest US sanctions against banks in the Islamic republic.

On Sunday the "historic defeat of the United States will be realised, and that came to be despite its attempts, trickery and extrajudicial moves," Khatibzadeh said.

"Iran again showed that the United States is not as all-powerful as it says," he added.

The embargo on the sale of arms to Iran is due to start expiring progressively from October 18, under the terms of a UN resolution that blessed the 2015 nuclear deal between the Islamic republic and world powers.

Washington suffered a setback in August when it failed to win support from the United Nations Security Council to indefinitely extend the embargo.

President Donald Trump unilaterally withdrew the United States from the nuclear deal in 2018 before reimposing US sanctions on Iran.

Since then, the US has slapped additional sanctions on Iran as part of a campaign of "maximum pressure", with the latest on Thursday concerning 18 banks.

"We used to say they are addicted to sanctions, but now they have reached insanity," Khatibzadeh said.

The spokesman added that the excessive use of sanctions had caused the Americans to "cannibalise" themselves, as well as prompted other countries to find alternatives to the US dollar.

The US claims that transactions involving humanitarian goods such as food and medicine are exempt and that sanctions are "directed at the regime".

Yet statements from experts and rights groups indicate the sanctions have had dire humanitarian consequences and caused suffering for the people of Iran.

In a speech on Monday, Iran's supreme leader Ayatollah Ali Khamenei pointed to the role of sanctions on Iran's troubled economy and called them "a crime in the true sense of the word."

He emphasised that the "cure" for the economy "should not be sought outside of the country", and called for the "focusing on production, preventing the continuous devaluation of national currency" and fighting smuggling and corruption.

"We will continue resisting so that, God willing, this maximum pressure will turn to maximum disgrace and a cause of regret for them," he said.