Anti-government demonstrators flooded the streets of cities in southern Iran on Friday after internet services were cut off, activists said.
Security forces surrounded a mosque at the centre of weekly rallies in the province of Baluch on the border with Pakistan. The region has been the focal point of an anti-government movement that started last September.
"We swear on our comrades' blood to stand strong until the end," hundreds of demonstrators could be heard chanting in a video from the flashpoint city of Zahedan posted by the activist news agency Hrana.
The Baluch Activists Campaign (BAC) posted footage on Telegram showing protesters brandishing placards with slogans including "Death to the dictator" as they marched through the capital of Sistan-Baluchistan province.
The province of Baluch has suffered repeated killings by security forces in recent years.
At least 66 people were killed in the deadliest crackdown since September 30, in Zahedan, according to Amnesty International.
The demonstrations were sparked by the death 22-year-old Kurdish-Iranian woman Mahsa Amini in police custody, She was arrested for breaking the country's strict hijab policy, which requires women to entirely cover their hair and bodies.
As with previous bouts of unrest, authorities appeared to have disrupted internet services on Friday.
"Confirmed: Real-time network data show a significant disruption to internet connectivity in Zahedan, #Iran; the incident comes amid a growing security presence during Friday protests," NetBlocks, an internet monitor, said.
Friday prayers at the city's main place of worship, the Grand Makki Mosque, have during the protest movement been marked by outspoken sermons by senior Sunni cleric Molavi Abdolhamid, who has supported the protesters and been bitterly critical of the authorities in Tehran.
Some reports suggested that the internet blocking was intended to prevent people from following his sermon online.
"Listen to the people and the opposition," activists including the BAC cited Mr Abdolhamid as telling the government in his latest sermon.
"If you cannot solve the problems of the people, step aside and let someone who can come and solve the problems," he said.
Iranian state media did not mention or publish a statement about Friday's reported protests. Tehran previously said the protests are being instigated by the government's foreign enemies.
While the nationwide unrest has diminished in recent weeks, probably because of executions and crackdowns, acts of civil disobedience have continued , from anti-government graffiti to unveiled women appearing in public.
With reporting from agencies