At least 11 miners have died after methane gas and coal dust exploded in a coal mine. The search continues for three other people.

The death toll at a coal mine in north-eastern Colombia has risen to at least 11.

A total of 14 people were missing after an explosion in the mine near the town of El Zulia in the department of Norte de Santander last week, as the South American country’s civil defense announced on Twitter on Monday. The other three people are still being sought.

An explosion of methane gas and coal dust caused landslides and a high concentration of carbon monoxide, the Colombian mining authority has now announced the cause of the accident.

According to media reports, the rescuers were initially unable to get to the 14 buried miners. The rescue was difficult because of the unstable shaft and the large concentration of gas. Therefore, according to the mining authority, large fans were set up.

The mine was closed due to another incident last year and was only recently allowed to resume operations, a spokesman for the local mining administration told the newspaper La Opinion. At that time it was about improving the ventilation in the mine. The mine near the border with neighboring Venezuela has been in operation for around 30 years, it said.

According to the newspaper “El Tiempo”, there have been around 140 accidents in mines in the Norte de Santander department since 2011, in which 149 miners died. In February, an explosion at a coal mine in the central Colombian municipality of Tasco killed 15 people.