Former Mayor of New York and US Presidential candidate Rudy Giuliani, 76, was speaking at the Free Iran Global Summit, the largest virtual gathering ever held.
The huge event witnessed thousands of Iranian opposition activists join in from more than 100 countries around the world.
Maryam Rajavi, leader of the People’s Mujahedin of Iran (MEK), an organisation trying to overthrow the Iranian government, was one of the key speakers.
She spoke from the summit headquarters at Ashraf-3 in Albania, where many of the movement are living in exile.
Joining the conference from the US, Giuliani, who is Donald Trump’s lawyer, claimed Rajavi to be the legitimate leader of Iran.
He dismissed critics who claimed the National Council of Resistance in Iran (NCRI), which organised Friday’s summit, is a “cult” and branded Ayatollah Khamenei a “tyrant”.
The veteran Republican also slammed Iran’s President Hassan Rouhani as the Ayatollah’s “puppet”.
He went on: “The NCRI and the MEK are the only ones who can replace the regime.”
In a move reminiscent of his client Trump, Giuliani hit out at what he described as “the corrupt western press” for suppressing the truth about Iran’s opposition, accusing them of “selling their souls to terror “.
Today’s groundbreaking summit also featured speakers from the British, French and German parliaments, as well as footage from gatherings of opposition activists around the world and music from Iranian musicians.
Giuliani hailed the gathering, held over Zoom, as demonstrating the enormous resistance to the Iranian government.
“This is a bridge to a democratic, free and prosperous Iran,” he said.
“The Iranian people deserve that and they can sustain that.”
He also claimed the Iranian economy was collapsing, in part due to the heavy sanctions placed on it by the Trump White House, and also because of coronavirus.
Singling out one particularly horrific event which stood with him from last years anti-regime protests, Giuliani highlighted seeing footage of a man trying to sell one of his kidneys for the equivalent of $ 400 (£319) to feed his starving family.
Slamming the actions of Barack Obama in signing the nuclear deal with Tehran, Giuliani said people were still starving even when the state was receiving billions from abroad.
Now, with the additional “crushing sanctions” introduced by Donald Trump as well as the coronavirus, the country was in the perfect condition for a revolution, he said.
He compared the Iranian regime to the last days of the Soviet Union, adding “they are on the brink”.
But, despite the crippling effects of sanctions and Covid-19, he accused Tehran of continuing to allocate huge sums of money abroad to fund global terrorism.
“This is a regime which would rather support terror than feed their people,” he said.
“Iran’s leaders are not just religious maniacs, they are common criminals.”
Referring to his time as a prosecutor in New York, he went on: “The Mullahs are like the people I prosecuted who ran the mafia. The Ayatollah is the head of the mafia.
“He is a mass murderer. How can he describe himself as a man of God?”
Giuliani added: “Regime change in Iran is within reach. Don’t listen to the pessimists. It will collapse overnight, like the Soviet Union.”
He finished: “Were going to wake up one morning and be surprised that the regime has fallen. It is teetering at the moment.”