Libya's interior ministry said in a statement on Tuesday that "outlaws" had attacked the border, which sees a large flow of Libyans often going to Tunisia for medical treatment and trucks with goods coming in the opposite direction.
"This action carried out by these outlaw groups will not be tolerated, and legal measures and the most severe penalties will be taken against those involved," the Tripoli-based ministry said, without giving further details.
Libya has had little peace since a 2011 uprising and is split between eastern and western factions, with rival administrations governing each area.
Unverified footage on social media showed a burning vehicle at Ras Jdir and people running, with the sound of gunfire.
The ministry said on Sunday it had deployed security forces at the border to combat smuggling and insecurity.
Tunisia's Tataouine Radio said late on Monday that Tunisia closed the crossing for the safety of citizens going to Libya.
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