Hezbollah on Monday struck an Israeli military position near the border to Lebanon, claiming it had done so in response to Israeli violations of the shaky ceasefire between the two sides.
The militia group described it as a "defensive warning strike" and cited various cases of shelling and artillery fire in Lebanon.
The IDF Israeli military said that Hezbollah launched two missiles but caused no casualties in the attack in the disputed Shebaa Farms area, also known as Mount Dov.
Israel's Prime Minister Benjamin Netanyahu condemned the attack.
"Hezbollah's firing at Mount Dov constitutes a serious violation of the ceasefire, and Israel will respond strongly to this," Netanyahu said. "We are determined to continue to enforce the ceasefire, and to respond to any violation by Hezbollah — minor or serious."
Netanyahu's defense minister, Israel Katz, also said the firing on an IDF post would be met with a "harsh response."
Lebanon reports 9 dead in strikes in south
Soon after these comments, the IDF said online in Hebrew that it was firing on "targets" in Lebanon, saying only that more details would follow later.
Late on Monday, Lebanon's Health Ministry gave what it described as a preliminary toll of nine dead and three wounded from strikes in the south of the country. It said five died in Haris and four in Tallouseh.
Lebanese authorities had also reported attacks in several locations earlier on Monday, saying two people had been killed in the southern area near the border.
Israel's military did not comment on these cases immediately, but did say a Lebanese army soldier was injured in one incident on Monday and said it was under review.
Negotiator Berri says more than 50 violations by Israel
Lebanon's speaker of parliament, Nabih Berri, an ally of Hezbollah's and core negotiator for Lebanon in the ceasefire talks, said Lebanon had so far logged at least 54 Israeli violations of the agreement.
Berri's office issued a statement urging the committee monitoring the ceasefire to "urgently" begin work and to "oblige" Israel to withdraw from Lebanese territory.
Pentagon says ceasefire holding, 'broadly speaking'
The ceasefire brokered between Israel, Hezbollah and Lebanon, which came into effect last week, foresees a 60-day pause in fighting during which time Hezbollah forces should move north, relatively far from the de facto border to Israel.
Israel's military should also withdraw from southern Lebanon by then, but for now Israeli politicians and soldiers say the IDF military is enforcing the terms of the ceasefire and responding to violations in the area.
Amid sporadic exchanges of fire on an almost daily basis, strain on the deal has been evident.
However, a spokesman at the Pentagon in the US said on Monday that despite breaches, the truce appeared to be holding for the most part.
"Broadly speaking, it is our assessment that despite some of these incidents that we are seeing, the ceasefire is holding," Air Force Major General Patrick Ryder told reporters.