Turkish officials have revised the death toll from Tuesday's mine disaster upward, to an estimated 300 people, with 18 miners are still trapped beneath the surface.

News sources report that 787 people were inside the mine at the time of the explosion, and that 20 of the 80 people injured were rescue workers.

Carbon monoxide poisoning is believed to be the cause of most of the fatalities.

The disaster led to widespread violent protests over mine safety conditions in Turkey and precipitated a political crisis for the country's Prime Minister, Recep Tayyip Erdogan.

The Labor Ministry said the mine has been regularly inspected -- most recently in March this year -- and that no irregularities had been detected.

A proposal to investigate previous deaths at the Soma mine was defeated in Turkey's parliament last month.

UPDATE FROM NBC NEWS: Turkey Mine Disaster Death Toll Likely to Top 300