Thirteen more bodies have been found during search and rescue operations at a coal mine in northeastern Iran, which was hit by an explosion caused by methane gas buildup last week.

Director General of Golestan Province’s Crisis Management Directorate, Sadeq-Ali Moqaddam, announced the development on Monday.

Accumulation of methane gas at the local mine in the province’s Azad-Shahr city triggered the blast last Wednesday.

“After rescue workers reached the site of the explosion in the second tunnel [dug for rescue purposes at the mine], they managed to reach 13 more bodies belonging to the miners. The workers are trying to take the bodies out,” the official said.

“Twenty-two bodies had already been found at the Yort mine. Including the bodies found on Sunday, the number of the fatalities has reached 35,” the official added.

Twenty-two of the fatalities have so far been taken out of the mine and handed over to their families, Moqaddam said.

'More fatalities likely'

The explosion has also left 73 other workers injured, according to estimates so far.

The official said search operations continue to see if the blast has caused any more human losses.

President Hassan traveled to the city on Sunday to address the situation and meet with the tragedy’s survivors and miners.

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The president called for the explosion to be investigated "so that such disasters do not repeat themselves in the future."

The mine, operated by the private sector, started its operations 13 years ago, amid reports that the equipment used in the pit was in dire need of repair or replacement.

“I had already received some reports about this mine concerning the contractor. Today, some new problems came to my attention," Ali Rabi’ei, the Iranian minister for cooperatives, labor, and social welfare, said on Sunday.

Picture taken on May 7, 2017 shows Ali Rabi’ei, the Iranian minister for cooperatives, labor, and social welfare (R), monitoring underway rescue operations at a coal mine in the northeastern Golestan Province. (Photo by Mehr News Agency)

Rabi’ei said the rescue operations could take five or six days or even longer.