A bus rented by Iranian medical students plunged into a ravine off a mountain road in the central Philippines, killing 20 people and injuring about 26 others, officials said on Monday.

The brakes apparently failed before the bus plummeted into a 100—foot (30—meter) ravine on Sunday in Balamban town in Cebu province, police Senior Superintendent Erson Digal said.

The Filipino driver and owner and 19 Iranians died, and 26 people were injured, said regional military spokesman Lt. Col. Wilson Feria.

Nine of an estimated 55 passengers were unaccounted for still, but the military was double—checking because it was unclear exactly how many people were on board, Mr. Feria said.

Villagers and police pulled bodies from the mangled wreckage at the rocky bottom of the ravine, while a backhoe sent by a nearby Japanese shipbuilding company attempted to lift the bus up, he said.

Cables were attached but the bus was too heavy and there was a danger the backhoe might be pulled down, he added.

The bus had an ominous plate number- DWZ—666, the “Number of the Beast” in the Bible’s Book of Revelation.

Many victims were medical students in Cebu, a bustling commercial and tourism centre 350 miles (560 kilometers) southeast of Manila. They were identified by relatives and through their IDs, Mr. Digal said.

Mr. Feria said it was not clear if the Iranians were involved in a medical mission or went for an outing at one of several resorts in and around Cebu.

Poorly maintained vehicles and roads, along with inadequate safety signs, railings, training and weak traffic law enforcement, are blamed for many deadly accidents in the Philippines.

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