Iranian police fired tear gas and warning shots to disperse protesters in the southwestern city of Abadan where a tower block collapse killed 29 people, local media reported on Saturday.
A large section of the 10-storey Metropol building that was under construction in Abadan, Khuzestan province, crumbled on Monday in one of Iran's deadliest such disasters in years.
It was the third night of protests in Abadan and other cities of the province which borders Iraq, local media reported.
Security forces in Abadan "used tear gas and shot in the air near the collapse site" on Friday night to disperse hundreds of protesters, who were mourning the lives lost and demanding justice for the perpetrators of the incident, Fars news agency said.
A number of people shouted "death to incompetent officials" and "incompetent officials must be executed", similar to calls in protests on Wednesday and Thursday nights, it added.
Elsewhere in Khuzestan, another protest in the city of Bandar-e Mahshahr saw people chanting while banging on traditional drums and hitting cymbals, images published by Fars showed.
People also took to the streets further afield, including in the central Iranian cities of Isfahan, Yazd and Shahin Shahr on Friday, to express sympathy with the victims of the tragedy, Fars news agency said.
On Thursday night, a shop in Abadan belonging to the family of the building's owner "was set on fire and destroyed by unknown individuals", Tasnim news agency reported earlier.
The government has declared Sunday a day of mourning for the victims of the building collapse, state news agency IRNA said.
Interior Minister Ahmad Vahidi, who has travelled to Abadan, said Saturday that "two more bodies were recovered", while local governor Ehsan Abpaspour later said another corpse was found, raising the death toll to 29, according to IRNA.
Officials have said 37 people were injured, but they have not given a figure for those still trapped under the rubble.
The number of suspects has been on the rise.
Khuzestan's provincial judiciary said on Saturday that 13 people have now been arrested in connection with the incident, including the mayor and two former mayors, IRNA said.
In a statement posted on his official website on Thursday, Iran's supreme leader Ayatollah Ali Khamenei called for those responsible to be prosecuted and punished.
First Vice President Mohammad Mokhber told state television that "widespread corruption existed between the contractor, the builder, the supervisor and the licensing system".
In January 2017, 22 people, including 16 firefighters, died in a blaze that engulfed the 15-storey Plasco shopping centre in Tehran.