"Yes, Abdelati al-Obeidi was arrested today," Mahdi al-Harati, vice chairman of military council for fighters, said in Tripoli on Wednesday, AFP reported.
Obeidi was reportedly arrested in his farm in Janzour, a suburb west of Tripoli, Press TV reported.
Abdallah al-Hijazi, a close associate of Gaddafi, has been also arrested by opposition forces, sources from the Transitional National Council (TNC) said.
The TNC has also said that fighters have killed Gaddafi's son and the commander of Libya's most horrified brigade Khamis as well as the head of intelligence Abdullah al-Senussi.
Meanwhile, fighters held negotiations with Saadi Gaddafi, another son of the fugitive ruler, about his surrender following his claims in an audio interview with al-Arabia channel that he had "no problem" with revolutionary forces.
"He (Saadi) is reluctant, but if he wants to surrender, his life will be safe, God willing. If there is an agreement, there will be no problems," deputy chief of the fighters' military council Mehdi Harati said.
Saadi had said he would be ready to give himself up to stop more bloodshed in the country.