As protesters pour into the streets of Iran night after night, leaders across the region and around the world are grappling with the possibility that the Islamic Republic could be overthrown – a seminal event that would transform global geopolitics and energy markets.

The regime of Supreme Leader Ayatollah Ali Khamenei has weathered bouts of protests many times, but demonstrations that began two weeks ago are spreading. By some accounts, hundreds of thousands defied authorities’ threats and a brutal crackdown to take to the streets over the weekend, from the capital Tehran to dozens of other cities across the nation of 90 million.

A protester burns an image of Iran’s Supreme Leader Ayatollah Ali Khamenei at a rally in Paris.Credit: AP

They are being cheered on by US President Donald Trump, fresh from the capture of Venezuela’s former president Nicolás Maduro. The US leader has in recent days repeatedly threatened to strike Iran, suggesting that America is back in the regime change business.

World leaders and investors are watching closely. US commanders have briefed Trump on options for military strikes, a White House official said. Brent crude surged more than 5 per cent on Thursday and Friday to more than $US63 a barrel as investors priced in the possibility of supply disruptions in OPEC’s fourth-biggest producer.

“This is the biggest moment in Iran since 1979,” former CIA senior Middle East analyst William Usher said, referring to the revolution that gave birth to the Islamic Republic, upended the balance of power in the region and led to decades of rancour between Tehran and the US and its allies.

“The regime is in a very tough spot right now, and the primary driver is the economy. I think they have a narrowing window to reassert control and a diminished tool set to do it.”

Anti-Shah protesters rally in Tehran in 1978, ahead of the return of Ayatollah Khomeini from exile and the ushering in of the Islamic Republic.Credit: AP

More than 500 protesters have been killed in the past two weeks, according to the US-based Human Rights Activists News Agency, and more than 10,000 have been arrested in demonstrations triggered by the currency crisis and economic collapse, but now also focused on the regime.

The authorities have tried to block the internet and phone networks since Thursday, as they seek to quell Iranians’ growing outrage over government corruption, economic mismanagement and repression. Foreign airlines have cancelled flights to the country.

Late on Monday........

© The Sydney Morning Herald