Forces loyal to Libyan leader Moammar Gadhafi clashed with Tunisian soldiers Friday, after crossing the border while pursuing rebel fighters.
Witnesses say Tunisian forces fought back, pushing the pro-Gadhafi soldiers back into Libya.
Libyan forces have been trying to reclaim the border crossing, in the western Wazin region, which was seized by rebels last week.
Tunisian officials say thousands of Libyans have fled to Tunisia during the past few days to escape the fighting.
Heavy fighting was also reported around the airport in the city of Misrata Friday, one of the few areas of the Mediterranean port town still controlled by pro-government forces.
In an earlier development, the U.S. envoy to the United Nations said Thursday that some pro-government fighters have been issued the anti-impotency drug Viagra, encouraging them to rape civilians.
Diplomats say U.S. ambassador Susan Rice brought up the shocking allegation during a closed-door meeting of the U.N. Security Council. They say Rice did not give any sources for the claim, and that it was brought up to highlight the brutality of Libyan leader Moammar Gadhafi's government.
Some information for this report was provided by AP, AFP and Reuters.