Six Libyan soldiers were killed in an attack by unidentified gunmen on an army checkpoint south of the coastal city of Sirte, once a stronghold of slain leader Muammar Gaddafi, a Libyan security source said on Tuesday.

There was no immediate word on who was behind the attack.

Sirte was the last city to fall to rebels who ousted Gaddafi in a civil war in 2011. The Libyan ruler, who had fled to Sirte when rebels overran the capital, Tripoli, was killed nearby.

Many civilians were displaced from the devastated city during and after the conflict. Residents complain of neglect.

"No one, only God, is taking care of the city - no army, no security," said one disgruntled citizen in Sirte. "The police are sleeping and their chief is sitting in Benghazi."

The Libyan government has struggled to control former rebel groups and Islamist fighters who have gained strength amid the turbulence plaguing the country since Gaddafi's overthrow.