There have been no claims of responsibility for the bombing.
Libya is caught in a conflict between two rival governments and scores of armed factions that back them. Islamist fighters allied with Islamic State are also present.
The source said the bomb targeted the Mislattah checkpoint near Khoms, on the coast road between Tripoli and Misrata.
Four years after a NATO-backed rebellion toppled Muammar Gaddafi, Tripoli is controlled by one alliance of former rebels and fighters who have set up their own self-proclaimed government and reinstated the old parliament.
Libya`s internationally recognized government and elected parliament have operated in the east of the country since an armed faction called Libya Dawn took over Tripoli last year.
The United Nations is trying to negotiate a peace agreement to form a unity government between the two rival factions. But hardliners on both sides have been resisting the accord and sporadic fighting continues.
Car bomb kills five at checkpoint east of Libya`s Tripoli
24 November 2015
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At least five guards in Libya allied with the self-declared government controlling Tripoli were killed and 16 others wounded when a car bomb exploded at a checkpoint east of the capital, a security source said on Tuesday.
