Sudanese officials say a gold mine accident has killed at least 60 miners in the western region of Darfur.

Authorities said the gold mine collapsed in the Jebel Amir district on Monday and word had only reached the Sudanese capital, Khartoum on Thursday. They said rescuers were trying to reach an unknown number of miners still trapped underground.

 

It was not immediately clear what caused the accident.

Sudan has been expanding gold mining as an alternative revenue source since losing most of its oil production in 2011, when South Sudan seceded. Khartoum earned at least $2.2 billion from gold exports last year.

Rival tribes fought each other over access to gold mines in Jebel Amir earlier this year. The fighting killed at least 400 people.

Years of tribal unrest and civil war in Darfur have prevented large-scale investments in its gold mines. Most gold producers in the Sudanese region are small companies that often operate in unsafe pits.