At least 22 people were killed and 40 others injured when a passenger bus plunged down some 200 meters from a highway in Nepal's far-western Jajarkot district on Thursday.Chief District Officer Krishna Chandra Poudel said 13 people died instantly and nine succumbed to their injuries in a hospital. The bus was heading from Khalanga to Khara, a village in the district.The bus with over 60 passengers was passing through rough terrain when the tragedy occurred.District police chief Bhabesh Rimal said a large number of security personnel have been deployed in the rescue work.Some of the seriously injured were taken to Kathmandu and Nepalganj for treatment.Bus accidents claim a large number of lives in Nepal every year due to the difficult terrain, untrained drivers and ageing vehicles.