Muhammad Salah Zuari, known as Abu Salim Taha, who is in custody in Lebanon and is the group's spokesman, said Fath al-Islam was part of al-Qaeda rather than a Syrian special forces' team, as claimed by the official Lebanese security services.
The newspaper said among evidence backing up the claims was the discovery of documents on the body of the group leader's son-in-law killed at the Iraqi border by Syrian troops.
The group based in northern Lebanon at the Nahr al-Bared Palestinian refugee camp comprised Lebanese, Syrian, Saudi Arabian, Iraqi, Jordanian, Yemeni, and North African nationals.
The conflict between the Lebanese Army and Fath al-Islam started May 20 and lasted for over three months, claiming the lives of 168 Lebanese soldiers and 220 militants. Some 200 militants were detained.
Shaker al-Abssi, the group leader from Jordan, managed to escape and is now being sought by Lebanese, Syrian, and Jordanian authorities.