Rudy Giuliani, the former Mayor of New York, made his comments to a crowd at a hotel in Times Square where he was attending the Iran Uprising Summit held by the Organisation of Iranian-American communities, which opposes the current regime in Tehran.
He said: “I don’t know when we’re going to overthrow them.
“It could be in a few days, months, a couple of years. But it’s going to happen.”
However, John Bolton, Donald Trump’s National Security Adviser, has stated it is against US policy to seek “regime change” in Iran.
Mr Giuliani nevertheless praised the sanctions and stated that they are “working”.
He said: “The people of Iran obviously have had enough now.
“The sanctions are working.
“The currency is going to nothing; these are the kinds of conditions that lead to successful revolution.”
The US State Department has reiterated that Mr Giuliani does not speak for the US administration.
Trump is nevertheless aiming to persuade Iran to curb its nuclear program and support for militia groups across the Middle East by virtue of his economic sanctions.
The US administration intends to implement further tariffs on the country’s oil industry on November 4, after withdrawing from the Iran nuclear deal in May.
Iran has claimed is has not broken the 2015 accord, and stated it has complied with the agreement between Tehran, the US and five other world powers.
The UN Atomic Watchdog also stated in August that Iran remained within the main restrictions of the agreement.
Ayatollah Ali Khamenei, Supreme Leader of Iran, has nevertheless shot back at the US over their ongoing actions.
He accused Gulf states backed by the US of attacking an Iranian military parade on Saturday, killing 25 people.
However he did not confirm which Gulf states he thought were to blame.