The United National Force in Lebanon (UNFIL) issued a statement on Wednesday protesting at the Israeli army's "intentional firing of three smoke rounds" in the occupied Shibaa Farms region last Friday.
The senior adviser to UNFIL, Milos Stugar, confirmed the attack - which occurred as occupation forces began an exchange of fire with Hizb Allah resistance fighters.
UNIFIL monitors the "Blue Line" southern frontier.
Hizb Allah said it had ambushed Israeli troops when they crossed the UN-drawn Blue Line, which marks where Israel withdrew from south Lebanon in 2000 after a 22-year occupation.
UNIFIL was established in 1978 after an Israeli incursion into south Lebanon.
It has 2000 international peacekeeping troops in Lebanon.