TEHRAN, Iran 

The Iranian government on Sunday declared a day of national mourning over last week's building collapse in the southwestern city of Abadan in which 29 people were killed.

In the capital Tehran, the municipality put black banners on all main streets and roundabouts with messages such as "Condolences Abadan" to express solidarity with people in Khuzestan province.

The ten-story Metropol commercial building collapsed on May 23 in what has been described by experts and disaster management authorities as one of the deadliest disasters in Iran in recent years.

The death toll has reached 29, which is likely to mount as more than 38 people are still missing, according to provincial authorities.

Iran's Interior Minister Ahmad Vahedi, who visited the site on Friday, said there might be a delay in operation to recover the dead bodies as the volume of debris is huge.

More than 100 people were present inside the under-construction building on the busy Amiri Street at the time of the collapse, Anadolu Agency learned from local sources.

The office of the provincial prosecutor in Khuzestan has announced the arrest of 13 people so far, including the mayor and deputy mayor, and a seven-member committee is undertaking a probe into the collapse.

The incident has raised alarm bells across the country, with people seeking stringent action against those responsible for the building collapse and mismanagement.

According to reports, there are around 33,000 to 34,000 buildings deemed unsafe in Tehran alone, of which more than 100 buildings are in "very dangerous conditions."