The National Transitional Council in Libya says Colonel Muammar Gaddafi's former intelligence chief Abdullah al-Senussi has been captured in southern Libya.
The southern Wadi Shati military council said Senussi did not put up any resistance and was arrested at his sister's home in the Al-Guira region on Sunday.
The International Criminal Court at The Hague issued a warrant on 27 June against Senussi on charges of crimes against humanity.
The ICC accuses Senussi, 62, of being an "indirect perpetrator of crimes against humanity of murder and persecution based on political grounds" committed in Benghazi from 15 - 20 February.
He was described by the ICC as "one of the most powerful and efficient organs of repression of Muammar Gaddafi's regime".
Senussi is also wanted in France where a Paris court sentenced him in absentia to life in 1999 over an attack on a French UTA airliner a decade earlier that killed 170 people.
Libya's interim rulers also announced Colonel Gaddafi's son Seif al-Islam would be tried inside Libya rather than by the International Criminal Court at The Hague.
On Saturday, the ICC said Libya must hand over Seif, but held out the prospect of a trial in Tripoli.
Seif, 39, was caught in the south of Libya in the Sahara early on Saturday.