(CNN) -- The U.S. State Department's latest travel warning for Libya still advises U.S. citizens "against all but essential travel to Tripoli and all travel to Benghazi," citing ongoing instability and violence, but says non-emergency U.S. government personnel can return to the U.S. Embassy in Tripoli.

The State Department had ordered all non-emergency U.S. government workers out of Libya on September 12, the day after an attack that killed four Americans -- including U.S. Ambassador Chris Stevens -- at a U.S. diplomatic mission in Benghazi.

Though the non-emergency personnel can return to the Embassy, they cannot bring their families "due to security concerns."

The warning also urges Americans not to travel to Bani Walid and southern Libya. "Because of ongoing instability and violence, the department's ability to provide consular services to U.S. citizens in these regions of Libya is extremely limited," the warning states.