Protesters set fire to tyres and blocked the road between Ben Guerdane and the border crossing of Ras Jedir about 30 kilometres (20 miles) away.
Protesters set fire to tyres and blocked the road between Ben Guerdane and the border crossing of Ras Jedir about 30 kilometres (20 miles) away, they said.
They gathered outside official buildings in Ben Guerdane and security forces intervened after they were targeted by stone-throwers, witnesses said.
Private radio station Mosaique FM reported the police fired tear gas to break up the protest.
The interior ministry told AFP police broke up a "protest of around 150 people" in a "legal way".
There were no immediate reports of any arrests or casualties.
Ras Jedir is the main crossing between western Libya and southeastern Tunisia, a region whose economy is largely dependent on cross-border trade, both legal and illegal.
Tensions have been high in recent months, with a part of the population accusing the authorities of ignoring their plight.
The authorities have said the issue is thorny in view of the political chaos and fighting between militias in Libya.
In May last year, security forces used tear gas against hundreds of people in Ben Guerdane protesting against the closure of the Ras Jedir crossing by Libyan authorities.
Two months earlier, Tunisia closed two border crossings with Libya for a fortnight in response to a deadly jihadist attack on Ben Guerdane.
Thousands of Tunisians are believed to be fighting with jihadist groups abroad including in Libya.