The Israeli army said Thursday it was conducting strikes on southern Lebanon after a mortar launched from its northern neighbour exploded in the border area between the two foes.
The latest military action comes three months after the two countries saw their worst cross-border fire in years.
It also comes amid rising tension between Israel and Arab countries after Israel carried out its biggest military operation in years in the occupied West Bank targeting the Jenin refugee camp, a Palestinian militant stronghold.
"A launch was carried out from Lebanese territory which exploded adjacent to the border in Israeli territory," an Israeli army statement said.
An army spokesman said the projectile was a mortar, after an army statement earlier reported the explosion had hit near the border town of Ghajar.
"In response, the IDF (Israeli military) is currently striking the area from which the launch was carried out in Lebanese territory," an army spokesman told AFP.
Lebanon's official National News Agency said Israel had fired "more than 15 artillery shells" which hit around the communities of Kfar Chouba and Halta.
The two countries are still technically at war, and peacekeepers from the United Nations Interim Force in Lebanon (UNIFIL) patrol the border between them.
Earlier on Thursday, Lebanon's armed Hezbollah movement denounced Israel for building a concrete wall around Ghajar, a small town that straddles their common border.
The Iran-backed Shiite group called on the Lebanese state to take action to "prevent the consolidation of this occupation" by Israel of Ghajar, home to around 3,000 people.
Hezbollah denounced Israel for the erection of "a barbed wire fence and the construction of a concrete wall around the entire locality".
- Rockets and drones -
Thursday's cross-border fire follows Israel bombarding Lebanon in April, in response to a barrage of rockets fired from the country.
The April incident was the heaviest rocket fire from Lebanon since Israel fought a war with Hezbollah in 2006.
UNIFIL, which was established in 1978, was beefed up in response to that 34-day conflict.
Last month, Hezbollah said it shot down an Israeli drone that had flown into Lebanon's southern airspace.
Israeli warplanes and drones regularly violate Lebanon's airspace, while the powerful Shiite Muslim movement for years has been sending drones towards Israel.
Weeks earlier Hezbollah had put on a display of military might, with mock cross-border raids into Israel a few miles (kilometres) from the border.
The strikes on Lebanon come a day after Israel hit militant targets in the Gaza Strip, in response to rocket fire from the coastal Palestinian territory.
Projectiles were fired from Gaza as Israeli forces drew to an end a massive raid in the occupied West Bank, their largest such operation there in years.
Twelve Palestinians and one Israeli soldier were killed in the two-day raid on the northern city of Jenin and its adjacent refugee camp.
Israeli forces launched drone strikes and employed an army bulldozer to rip up streets in Jenin's refugee camp, prompting at least 3,000 residents to flee.
Hundreds of troops were involved in the raid, which the army said targeted fighters in the militant stronghold.
Israel has occupied the West Bank since the 1967 Six-Day War and has imposed a crippling blockade on Gaza since 2007, when the militant group Hamas took power.
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