BOGOTA, Colombia (AP) — Rescue operations at a coal mine in central Colombia that collapsed earlier this week ended Thursday and officials said the accident had left 21 workers dead.

The mine near the town of Sutatausa collapsed late Tuesday following an explosion that blocked several of its entrances. Rescue teams worked nonstop for more than 30 hours to find survivors and retrieve bodies.

Nicolás García, the governor of Cundinamarca province, said nine workers survived the accident and had been released from hospital, while the relatives of miners who were killed were receiving psychological support. Officials said all of the workers who were at the mine at the time of the accident had been accounted for.

Colombian Minister of Mines Irene Velez said Thursday that the explosion was caused by methane inside the mine. She said the complex would remain closed until officials investigate how the explosion occurred.

Mining accidents are common in Colombia, particularly in coal and gold mines. Last year 117 accidents were registered at mines throughout the country by the National Mining Agency, which says that 146 workers were killed in those incidents.