Unconfirmed reports say Col Gaddafi has been killed, and AFP obtained a mobile-phone image apparently showing his face covered in blood.
The reports came after transitional forces claimed control of Sirte, Col Gaddafi's birthplace.
The colonel was toppled in August after 42 years in power. The International Criminal Court is seeking his arrest.
Nato, which has been running a bombing campaign in Libya for months, said it carried out an air strike earlier on Thursday that hit two pro-Gaddafi vehicles near Sirte.
The head of the National Transitional Council (NTC) Mustafa Abdul Jalil is expected to give a national TV address soon.
Information Minister Mahmoud Shammam says fighters on the ground have told him that Col Gaddafi is dead.
