Over two weeks of protests mark the most serious challenge in years to Iran's theocratic leadership in their scale and nature, but it is too early to predict the immediate demise of the Islamic republic, analysts say.
The demonstrations moved from protesting economic grievances to demanding a wholesale change from the clerical system that has ruled Iran since the 1979 revolution that ousted the shah.
The authorities have unleashed a crackdown that, according to rights groups, has left hundreds dead while the rule of Supreme Leader Ayatollah Ali Khamenei, now 86, remains intact.
"These protests arguably represent the most serious challenge to the Islamic republic in years, both in scale and in their increasingly explicit political demands," according to Professor Nicole Grajewski of the Sciences Po Centre for International Studies in Paris.
She said it was unclear if the demonstrations would unseat the leadership, pointing to "the sheer depth and resilience of Iran's repressive apparatus".
Authorities organised counter rallies, with thousands of people in attendance.
Professor Thomas Juneau, of the University of Ottawa, said: "At this point, I still don't assess that the fall of the regime is imminent. That said, I am less confident in this assessment than in the past."
These are the key factors seen by analysts as determining whether the leadership will hold on to power.
A key factor is "simply the size of protests; they are growing but have not reached the critical mass that would represent a point of no return," Prof Juneau said.
The protest movement began with strikes at the Tehran bazaar on 28 December and were followed by mass rallies in the capital and other cities.
The last major demonstrations, in 2022 and 2023, were sparked by the death in custody of Mahsa Amini. She had been arrested for allegedly violating the Islamic dress code for women.
In 2009, mass rallies took place after disputed elections.
But a multi-day internet shutdown imposed by Iranian authorities has hampered the ability to determine the magnitude of the current demonstrations, with fewer videos emerging.
Lecturer at Yale University, Arash Azizi, said: "The protesters still suffer from not having durable organised networks that can withstand oppression".
He said one option would be to "organise strikes in a strategic sector" but this required leadership that was still lacking.
Watch: What is happening in Iran?
While the situation on the streets is of paramount importance, analysts say there is little chance of a change without cracks and defections in the regime and the security forces.
So far there has been no sign of this, with the pillars of the country - from parliament to the president to the Revolutionary Guards (IRGC) - lining up behind Mr Khamenei's defiant line.
"At present, there are no clear signs of military defections or high-level elite splits within the regime. Historically, those are critical indicators of whether a protest movement can translate into regime collapse," Prof Grajewski said.
The Policy Director at United Against Nuclear Iran, a US-based group, described the protests as "historic".
However, Jason Brodsky added: "It's going to take a few different ingredients for the regime to fall," including "defections in the security services and cracks in the Islamic republic's political elite".
Israeli or US military intervention
US President Donald Trump, who has threatened military retaliation over the crackdown, announced 25% against Iran's trading partners.
The White House said that he was prioritising a diplomatic response, and has not ruled out strikes, after briefly joined Israel's 12-day war against Iran last June.
It resulted in the killing of several top Iranian security officials, forced Mr Khamenei to go into hiding and revealed Israel's deep intelligence penetration of the country.
US strikes would upend the situation, analysts said.
The Iranian foreign ministry said that it has channels of communication open with Washington despite the lack of diplomatic relations.
"A direct US military intervention would fundamentally alter the trajectory of the crisis," Prof Grajewski said.
"The regime is more vulnerable than it has been, domestically and geopolitically, since the worst years of the Iran-Iraq war" that lasted from 1980-1988, according to Prof Juneau.
The US-based son of the ousted shah, Reza Pahlavi, has taken a major role in calling for protests and pro-monarchy slogans have been common chants.
But with no real political opposition remaining inside Iran, the diaspora remains critically divided between political factions known for fighting each other as much as the state.
"There needs to be a leadership coalition that truly represents a broad swathe of Iranians and not just one political faction," Mr Azizi said.
Mr Khamenei has been in power since 1989 when he became supreme leader, a post for life, following the death of revolutionary founder Ruhollah Khomeini.
But uncertainty has long reigned over who could succeed him, with options including his son Mojtaba or power gravitating to a committee rather than an individual.
Such a scenario between the status quo and a complete change could see "a more or less formal takeover by the Revolutionary Guards", Prof Juneau said.
