An explosion caused by a gas leak at a coal mine in eastern Iran has killed at least 51 people, state media said on Sunday.

More than 20 others were injured after the blast in South Khorasan province.

It is reported to have been caused by a methane gas explosion in two blocks of the mine in Tabas, 540 km (335 miles) southeast of the capital Tehran.

The explosion occurred at 21:00 local time (17:30 GMT) on Saturday, state media said.

South Khorasan's governor Javad Ghenaatzadeh said there were 69 workers in the blocks at the time of the explosion.

According to the AP news agency, he said: "There was an explosion and unfortunately 69 people were working in the B and C blocks of Madanjoo mine.

"In block C there were 22 people and in block B there were 47 people."

It remains unclear how many people are still alive and trapped inside the mine.

State media has now revised its earlier toll of 30 dead.

"The number of dead workers increased to 51 and the number of injured increased to 20," the official IRNA news agency reported.

Citing the head of Iran's Red Crescent, state TV said earlier on Sunday that 24 people were missing.

According to Reuters news agency, Iranian 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.