TEHRAN, Iran — Rescue teams in the Iranian capital worked through the night and into the day Friday to try and reach firefighters and other victims believed to be under the rubble of a commercial building that collapsed in Tehran the previous day.

Iranian officials have yet to offer definitive casualty figures for the disaster. Iran’s state-run Press TV reported on Thursday that 30 firefighters had been killed, without elaborating.

Later Thursday, Tehran Mayor Mohammad Bagher Ghalibaf said more than 20 firefighters had been killed and promised further updates. Ghalibaf also said there were no civilians inside the building at the time of the collapse, though witnesses said people had slipped through a police cordon to try and save their valuables inside the burning building.

On Friday, authorities said an injured firefighter died at a local hospital. No survivors or bodies have been pulled out of the rubble so far.

The disaster had stunned many Iranians and triggered an outpouring of grief across Tehran.

Iran’s government announced that Saturday would be a day of mourning for the nation following the incident that “claimed lives of several people and brave firefighters,” according to a statement carried by the official IRNA news agency.

Jalal Maleki, spokesman of the Tehran Fire Department, told state TV that along with firefighters who are believed to be under the rubble, “we assume that there are some other people.”

Iranian media said Behnam Mirzakhani, one of the firefighters hospitalized in Tehran, died Friday from his injuries sustained in the building’s collapse.