At least 15 people were killed and 30 others injured when an oil tanker exploded in Afghanistan's Parwan province, a senior official said on Thursday.The incident occurred late Wednesday night in the provincial capital of Charikar after a bomb attached to the tanker exploded, the official told Xinhua news agency. "The number of the casualties may rise as several injured were in critical condition," he said.No group has claimed responsibility for the attack yet.