The incident occurred near the town of Aytaroun on Saturday.
UNIFIL condemned the attack on its peacekeepers and called it "deeply troubling".
“We strongly remind the parties of their obligations to protect peacekeepers and avoid putting the men and women who are working to restore stability at risk,” it said in a statement.
The attack came days after Israeli fighter jets bombed a team of journalists with Al Mayadeen television network in southern Lebanon on Tuesday.
The network’s correspondent Farah Omar and cameraman Rabih Maamari were killed in the attack.
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