“We responded with fire, & our aircraft struck Hezbollah observation posts near the border. This is a severe event & we remain ready to combat any threat to our borders.”
No Israeli soldiers were wounded in the firing, the military added.
Soldiers deployed illumination flares, smoke shells and live fire after the shots from the Lebanese side of the frontier, it said.
Set up in 1978, UNIFIL was beefed up after a month-long devastating war in 2006 between Israel and Hezbollah.
The 10,500-strong force, in coordination with the Lebanese army, is tasked with monitoring a ceasefire and Israeli pullout from a demilitarised zone on the border.
Israel accuses Hezbollah of stockpiling weapons at the border to prepare for a new war.