"An Israeli drone... violated Lebanese airspace over the Bastra farms" in southern Lebanon, the army said in a statement.
"It released incendiary substances on oak trees in the area, which resulted in a blaze," it added. There were no reports of injuries.
An Israeli military spokeswoman said the blaze that erupted near a demarcation line between the two countries was caused by army "operations" in the area.
"A short while ago fires erupted adjacent to the Blue Line between Israel and Lebanonand the fires are a result of IDF operations in the area," she told AFP without providing additional details.
The incident comes amid heightened tensions between the two neighbours, after Lebanon accused Israel of targeting a stronghold of the Shia Hezbollah movement with explosive-laden drones last week.
Israel's arch-foe Hezbollah said the August 25 drone attack had "hit a specific area," without elaborating on the nature of the target.
Hezbollah chief Hassan Nasrallah said Saturday his group's response to the incident had been "decided".
"The need for a response is decided," he said during a televised speech, adding it was about "establishing the rules of engagement and... the logic of protection for the country".
Israel "must pay a price", he said.
He vowed to retaliate "at all costs" and target Israeli drones, which often operate in Lebanese airspace.
In a rare incident on Wednesday, the Lebanese army opened fire on Israeli drones that had violated Lebanon's airspace, forcing the aircraft to return across the border.
On Saturday, Israel fired flares over several areas close to the border, one of which landed in a base run by an Indian battalion of UN peacekeepers, according to the UN and the Lebanese army.
Israel and Hezbollah have fought several wars, the most recent a 33-day conflict in 2006, which killed 1,200 people in Lebanon, mostly civilians, and 160 Israelis, mostly soldiers.
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