Antioquia state disaster coordinator John Rendon says about 40 workers are still underground. Officials hold out little hope any remain alive.

Rescuers carried out 13 bodies on Sunday from deep inside the 2-kilometer access tunnel at the San Fernando mine in northwest Colombia. They found two more Monday. The blast occurred last Wednesday.

Rendon says debris and the persistent buildup of methane and carbon monoxide gases continue to impede rescue efforts.

The exact cause of the explosion is unknown, but the mine's records indicate it lacked a methane ventilation pipe and gas-detection device.

AP