A security source said on Tuesday at least five guards were killed and another 16 wounded east of the Libyan capital at a checkpoint.
The guards are allied with the self-declared government controlling Tripoli.
No one claimed responsibility for the bombing which targeted the Mislattah checkpoint near Khoms, on the coastal road between Tripoli and Misrata.
After Libya's dictator Muammar al Gaddafi four years ago was deposed and killed by NATO-backed rebels, Libya fell into chaos as fighting between factions broke out. There are currently two rival self-declared governments controlling different areas of the country backed by armed militias - the House of Representatives (HoR) based in Tobruk and the General National Assembly based in Libya's capital Tripoli.
Some DAESH terrorists are also active in the region.
The Libyan Army was disbanded following the 2011 ouster of former long-term autocrat Muammar al-Ghaddafi and militias loyal to Haftar declared themselves to be the “Libyan National Army” last summer after joining an alliance with the HoR based in Tobruk.
Some areas of Libya are not under the control of either of the two governments.
The United Nations has attempted to unify the two rival governments of Tripoli and Tobruk and reach a peace agreement, but no accord has yet been reached and the fighting between the two sides is continuing.