Major Iranian cities were gripped overnight by new mass rallies denouncing the Islamic republic, as the son of the ousted shah urged protesters on Saturday to plan to seize city centres.
The two weeks of protests have posed one of the biggest challenges to the theocratic authorities who have ruled Iran since the 1979 Islamic revolution, although supreme leader Ayatollah Ali Khamenei has expressed defiance and blamed the United States.
Following the movement's largest protests yet on Thursday, new demonstrations took place late Friday, according to images verified by AFP and other videos published on social media.
This was despite an internet shutdown imposed by the authorities, with monitor Netblocks saying early Saturday that "metrics show the nationwide internet blackout remains in place at 36 hours".
In Tehran's Saadatabad district, people banged pots and chanted anti-government slogans including "death to Khamenei" as cars honked in support, a video verified by AFP showed.
Other images disseminated on social media and by Persian-language television channels based outside Iran showed similar large protests elsewhere in the capital, as well as in the eastern city of Mashhad, Tabriz in the north and the holy city of Qom.
In the western city of Hamedan, a man was shown waving a shah-era Iranian flag featuring the lion and the sun amid fires and people dancing.
In the Pounak district of northern Iran, people were shown dancing round a fire in the middle of a highway, while in the Vakilabad district of Mashhad, a city home to one of the holiest shrines in Shiite Islam, people marched down an avenue chanting "death to Khamenei". It was not possible to immediately verify the videos.
- 'Big trouble' -
Reza Pahlavi, the US-based son of Iran's ousted shah, hailed the "magnificent" turnout on Friday and urged Iranians to stage more targeted protests this Saturday and Sunday.
"Our goal is no longer just to take to the streets. The goal is to prepare to seize and hold city centres," Pahlavi said in a video message on social media.
Pahlavi, whose father Mohammad Reza Pahlavi was ousted by the 1979 revolution and died in 1980, added he was also "preparing to return to my homeland" at a time that he believed was "very near".
Activists have expressed concern that the internet shutdown could mask repression by authorities, and the Norway-based Iran Human Rights group has said at least 51 people have been killed in the crackdown so far.
Iranian Nobel Peace Prize winner Shirin Ebadi warned on Friday that security forces could be preparing to commit a "massacre under the cover of a sweeping communications blackout".
Authorities say several members of the security forces have been killed, and Khamenei in a defiant speech on Friday lashed out at "vandals" and vowed the Islamic republic would "not back down".
He blamed the US for stoking the unrest in comments echoed by several other Iranian officials.
US President Donald Trump again refused on Friday to rule out new military action against Iran after Washington backed and joined Israel's 12-day war against the Islamic republic in June.
"Iran's in big trouble. It looks to me that the people are taking over certain cities that nobody thought were really possible just a few weeks ago," Trump said.
Asked about his message to Iran's leaders, Trump said: "You better not start shooting because we'll start shooting too."