Videos verified by the BBC and eyewitness accounts appeared to show the government was ramping up its response to the protests, which have spread to more than 100 cities and towns across every province in Iran.
US President Donald Trump has threatened to hit Iran "very hard" if they "start killing people".
Iran's parliament speaker warned on Saturday that if the US attacks, Israel and all US military and shipping bases in the region would be legitimate targets.
The protests were sparked by soaring inflation, and protesters are now calling for an end to the clerical rule of Iran's Supreme Leader Ayatollah Ali Khamenei.
Iran's attorney general said anyone protesting would be considered an "enemy of God" - an offence that carries the death penalty - while Khamenei has dismissed demonstrators as a "bunch of vandals" seeking to "please" Trump.
Trump on Saturday said the US "stands ready to help" as Iran "is looking at FREEDOM".
As protests intensify, the number of deaths and injuries continues to rise. Two human rights groups have reported more than 100 people, including security personnel, killed.
Staff at several hospitals told the BBC they have been overwhelmed with the injured and dead, with BBC Persian verifying 70 bodies brought to one hospital in Rasht city on Friday night and a health worker reporting around 38 people dying at a Tehran hospital.
Iran's police chief said on state TV that the level of confrontation with protesters had been stepped up, with arrests on Saturday night of what he called "key figures". He blamed a "significant proportion of fatalities" on "trained and directed individuals", not security forces, but did not give specific details.
More than 2,500 people have been arrested since protests began on 28 December, according to a human rights group.
The BBC and most other international news organisations are unable to report from inside Iran, and the Iranian government has imposed an internet shutdown since Thursday, making obtaining and verifying information difficult.
Nonetheless, some video footage has emerged, and the BBC has spoken to people on the ground.
Several videos, confirmed as recent by BBC Verify, show clashes between protesters and security forces in Mashhad, Iran's second largest city.
Masked protesters are seen taking cover behind bins and bonfires, while a row of security forces is seen in the distance. A vehicle that appears to be a bus is engulfed in flames.
Multiple gunshots and what sounds like banging on pots and pans can be heard.
A figure standing on a nearby footbridge appears to fire multiple gunshots in several directions as a couple of people take cover behind a fence.
In Tehran, a verified video from Saturday night shows protesters also taking over the streets in the Gisha district.
Other verified videos from the capital show a large group of protesters and the sound of banging on pots in Punak Square, and a crowd of protesters marching on a road and calling for the end of the clerical establishment in the Heravi district.
Internet access in Iran is largely limited to a domestic intranet, with restricted links to the outside world. But during the current round of protests, authorities have for the first time severely restricted the domestic intranet.
An expert told BBC Persian the shutdown is more severe than during the "Women, Life, Freedom" uprising in 2022.
Alireza Manafi, an internet researcher, said the only likely way to connect to the outside world was via Starlink satellite internet, but warned users to exercise caution, as such connections could potentially be traced by the government.
