Some figures from the National Transitional Council (NTC) told news agencies Mutassim Gaddafi had been seized in the family's embattled hometown of Sirte.

However, officials in the NTC stronghold of Benghazi could not confirm the claims, which have sparked celebratory gunfire in several cities.

NTC forces say they now control most of Sirte, following fierce fighting. There have been false reports of the capture of senior Gaddafi figures in the past, including another son, Saif al-Islam, and Gaddafi spokesman Moussa Ibrahim. But if confirmed, Mutassim Gaddafi's capture would be a major breakthrough for the NTC.

He is a senior officer in Col Gaddafi's army and was a national security advisor to his father. The NTC would want to question him as to the whereabouts of his father and other family members such as Saif and another son Khamis - both in Col Gaddafi's inner circle - analysts say.

Col Gaddafi is believed to be somewhere in Libya's southern deserts. His supporters are also holding out in the town of Bani Walid.