Mussa Ibrahim, who served as the last spokesman for deposed Libyan leader Moammar Gaddafi, was arrested on Saturday southwest of the capital, the prime minister's office said.
"Mussa Ibrahim was arrested at a checkpoint in the town of Tarhuna," read a brief statement sent to journalists after rumours that he had been detained spread on social networking sites.
"He is being taken to Tripoli where he will be handed over to the pertinent authorities to begin questioning," the statement continued.
Deputy Prime Minister Mustafa Abu Shagur confirmed the news on microblogging site Twitter with the following post: "Criminal Mussa Ibrahim was arrested and he is now on his way to Tripoli."
Rumours of Ibrahim's arrest and that of other personalities of the former regime said to be fleeing from the besieged town of Bani Walid had swirled since Saturday morning but officials were unable to provide immediate confirmation.