The Himalayan newspaper said seven more people were injured in the incident.
The bus was traveling on the Siddhartha highway to Butwal from Pokhhara, about 120 miles from the capital of Kathmandu in the Himalayan state, when it went off the road and rolled into the river below.
A police official said 12 people died at the scene and two more died at a hospital. Those killed included the bus driver.
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