The FBI and Bureau of Alcohol, Tobacco and Firearms believe "some sort of explosive device" was used, MSNBC reported.
Earlier, there was speculation the blast may have had a mechanical cause. The car was reported to be a Lexus hybrid.
No other details were immediately available.
"We do know that he was very, very seriously injured," said Bill Trice, the attorney of the state's medical board. "Our board members are in shock and waiting to hear any news, and are very saddened and prayerful for him and his family."
