At least 17 persons were killed and 20 injured on Tuesday when a passenger bus veered some 300 metres off a hilly road in Nepal's Dhading district, police said.The bus was travelling from a village to the district headquarters of Dhadingbesi.Chief District Officer Bishow Prakash Subedi said the bodies of the victims including 10 men and four women were retrieved from the accident site.Six of the injured were in critical condition. They were airlifted to capital Kathmandu for treatment, Subedi added.The cause of the accident was not immediately known but the police believe it could be the result of a combination of an overloaded bus and the steep gravelled road.