Overcrowding may have been a factor in a deadly bus crash in Nepal on Tuesday. According to an official quoted by the DPA news agency, passengers may have been traveling on the roof of the bus when it slipped off a muddy road and plunged into a riverbank.

The crash, which occurred on a rural mountain road in the district of Dhading, killed at least 18 people and injured 13 more. The area had recently been hit by monsoon rains, creating muddy conditions on roads.