At least 15 people were killed and 19 injured Wednesday in a bus accident in eastern South Korea, Korean television reported. The bus carrying vacationers began to skid as it drove down a mountain road before crashing into a guard rail, plunging down a slope and overturning, KBS radio reported. Some of the victims had been trapped inside the wreckage, according to the report. The group was returning from a trip to the mountain resort of Pyeongchang to Seoul, about 180 kilometers to the west. Police said the high death toll was due to the fact that most of the passengers had not been wearing seat belts.