A gas explosion in a coal mine in Iran’s South Khorasan Province killed at least 51 people and injured 20, state media in the country said on Sunday.

The accident was caused by a methane gas explosion in two blocks, B and C, of the mine run by the Madanjoo company, state media said.

“Seventy-six percent of the country’s coal is provided from this region and around 8 to 10 big companies are working in the region including Madanjoo company,” the governor of South Khorasan Province, Ali Akbar Rahimi, told state TV on Sunday.

The rescue operation in block B has been completed. Of the 47 workers who were in the block 30 died and 17 were injured, Rahimi said earlier.

Rescue operations in block C have started. Methane density in the block is high and the operation will take around 3-4 hours, he added.

There were 69 workers in the blocks at the time of the explosion, state TV reported.

“Seventeen injured people were transported to the hospital and 24 people are still missing,” it said earlier on Sunday citing the head of Iran’s Red Crescent.

The explosion occurred at 9 p.m. (12:30 p.m. ET) on Saturday, state media said.

President Masoud Pezeshkian expressed condolences to the victims’ families. “I spoke with ministers and we will do our best to follow up,” Pezeshkian said in televised comments.