At least seven persons were killed and 18 other injured, when an overloaded jeep plunged into a 100-metre ravine in Nepal's Nawalparasi District on Sunday.The vehicle, which was heading for Kadabheri from Bulingtar in the district, slipped off a mountain highway, about 170 km from the capital city of Kathmandu."The condition of three injured, including the driver, was critical at a local hospital," Xinhua news agency quoted District Police Constable Kismat Balal Magar as saying.Nepal's Home Ministry officials said such accidents have been frequently taking place due to overloading and speeding."The local administration and police have been given stringent orders to control such practices," the ministry said in a statement.