A group with close links to the Libyan Muslim Brotherhood has denounced what it describes as an attack on the "legitimacy of the ballot box."

The statement, issued by Libya Rebels, came after retired general Khalifa Haftar launched an anti-Islamist offensive in Tripoli and Benghazi on Friday, vowing to cleanse Libya of the Muslim Brotherhood and other Islamist radicals.

"The time for coups is over," the group said, pledging to challenge "dreamers who attempt to win power with tanks."

The Libyan army's chief of staff has announced his commitment to preserving Libya's unity, stating recent events had spurred divisions within the country.