A commander of "Libya Shield" brigades said his soldiers took over a camp for Special Forces western the capital Tripoli.
He said the 27th camp take-over came after fierce clashes with militants.
He said his troops are waiting additional military reinforcement.
Violence is sweeping through Tripoli, and Libya's second largest city of Benghazi as rival groups have been involved in a power struggle since the overthrow of former leader Colonel Muammar Gaddafi in 2011.