A local official in the area said that nearly 70 people were injured.

The officials said that those killed were miners in a tunnel trying to reach 32 miners trapped underground in the northern province of Golestan.

The mine blast is thought to have been caused by a gas leak.

Emergency crews are at work at the scene of the disaster, and have so far cleared about 600m (1,960ft) of the tunnel leading to the mine, officials say.

But there has so far been no news about the condition of the trapped miners.

They are believed to be at least 1,300m (4,265ft) underground at the Zemestan-Yurt mine, near Azadshahr.

The men are said to have limited space and to be in danger from volatile gasses. Earlier reports said that at least 50 miners were buried by the blast.

It remains unclear exactly how many miners are affected - with the authorities issuing different numbers throughout Wednesday.

Two people were reported to have been killed earlier on Wednesday, with 25 others wounded by the blast.

One emergency services spokesman said that 16 people had managed to escape.

There are some reports that the gas explosion may have been caused by someone attempting to start a lorry engine.

President Hassan Rouhani meanwhile has been criticised by conservative rivals and the media for what they describe as his government's "slow response" to the disaster.

He has sent Labour Minister Ali Rabei to the scene.

The incident could have political consequences for the government - coming less than a month before the 19 May presidential election in which Mr Rouhani is facing a strong challenge from conservative candidate Ebrahim Raisi.

The rescue operation has reportedly been hampered by concerns about gas in the tunnels.

Hamidreza Montazeri, deputy head of the provincial emergency services, told PressTV earlier on Wednesday that 25 people involved in the rescue had been taken for treatment after inhaling gas.

State media reported that the mine employed some 500 workers and that the explosion - which took place at about 12:45 (09:45 GMT) - happened during a change of shift.

Iran, which extracted 1.68 million tonnes of coal in 2016, mostly uses coal for domestic steel production rather than exporting it.