A Facebook page purporting to belong to Ibrahim denied the capture, saying it was an effort to divert attention away from the "atrocities" being committed by the Libyan forces besieging Bani Walid. The site and statement could not be independently confirmed, but hours after the announcement of his capture, Ibrahim had not been seen in public.
Violence has flared periodically over the last year in Bani Walid, the most significant town in Libya still resisting the country's new authorities since the end of the country's civil war last year.
The urbane, English-speaking Ibrahim was the most well-known former regime figure to remain unaccounted for after Gadhafi was captured and killed by rebels as his hometown of Sirte was falling on Oct. 20, 2011, following an eight-month civil war.
Gadhafi's son and heir-apparent Seif al-Islam was captured by former rebels late last year. The regime's former intelligence chief Abdullah al-Senoussi fled the country but was later captured in Mauritania and extradited to Libya. The two men had been charged by the Hague-based International Criminal Court along with Gadhafi of attacking civilian protesters in the early days of the popular uprising. The case against Gadhafi was dropped after he was killed.
Other family members also fled to other countries, but their whereabouts are largely known.
The government statement added that Ibrahim was captured at one of the checkpoints outside Bani Walid, where fighting has raged for the past four days as government forces seek to retake the town.
Fighters of the pro-government Libya Shield militia have besieged the town, some 140 kilometers (90 miles) southeast of Tripoli, for the past several weeks, blaming residents for the death of a well-known anti-Gadhafi rebel.
An official at Misrata Hospital, who spoke on condition of anonymity because he was not authorized to speak to the media, said seven Libya Shield fighters were killed in Saturday's fighting and 120 injured.
Parts of Bani Walid, a collection of settlements in a well-guarded valley, are under government control, according to Mohammed al-Zubedi, a local official allied to Tripoli.
Residents in Bani Walid say the pro-government forces, which are comprised largely of the militias that overthrew Gadhafi a year, are indiscriminately shelling the town.