The Israeli military said early Sunday it was striking Hezbollah targets in Lebanon after identifying the group as "preparing to fire missiles and rockets toward Israeli territory."
"In a self-defense act to remove these threats, the [Israeli military] is striking terror targets in Lebanon, from which Hezbollah was planning to launch their attacks on Israeli civilians," Israeli military spokesman Daniel Hagari said.
The Israeli military also issued a warning for people close to Hezbollah areas to leave.
"Anyone who is near areas where Hezbollah operates should leave immediately to protect themselves and their families," it said in Arabic.
The military also warned Israelis to expect incoming missiles and drones launched by Iranian-backed militia from across the border. Shortly after the warning, sirens sounded in northern Israel.
Meanwhile, Lebanese media reported strikes in the south of the country, without immediately giving further details.
The Israeli attacks and warnings come amid fears that Iran and its allies have been preparing a retaliatory move after an Israeli strike in July killed Hezbollah commander Fuad Shukr in Beirut. Iran has also vowed a response after Hamas leader Ismail Haniyeh was assassinated in Tehran last month, which Iran blamed on Israel.
Hezbollah says it has begun retaliatory strike over death of top commander
Hezbollah said that, in response to the killing of its top commander in a Beirut suburb last month, it had launched an attack on Israel with a large number of drones and rockets.
The Lebanon-based group said it targeted an identified "special military target as well as Israel's Iron Dome platforms and other sites but that the full response would take "some time."
"The number of Katyusha rockets launched until now is more than 320 ... towards enemy positions," a Hezbollah statement said.
The group added that it had targeted 11 Israeli bases and barracks.
Iran-backed Hezbollah is considered a terrorist organization by the US, Germany and several Sunni Arab countries.
Israel says 'struck thousands' of Hezbollah rocket launchers
Israel's military said its fighter jets attacked thousands of Hezbollah rocket launchers in Lebanon that were aimed at northern and central Israel.
"Approximately 100 IAF fighter jets ... struck and destroyed thousands of Hezbollah rocket launcher barrels that were located and embedded in southern Lebanon," the military said in a statement.
"Most of these launchers were aimed toward northern Israel, and some were aimed toward central Israel."
Military spokesperson Lieutenant-Colonel Nadav Shoshani told reporters that Hezbollah in turn "fired hundreds of rockets and UAVs toward northern Israel."
Shoshani said the rockets were "part of a larger attack that was planned, and we were able to thwart a big part of it this morning," but he did not specify what Hezbollah had targeted.
"We're still in a situation assessment of the aftermath of the attack ... there is still some fire happening," he added.
Meanwhile, Lebanon's state-run National News Agency said that one person had died in an Israeli strike on a vehicle in the town of Khiam.
Local media in Lebanon also reported other strikes across the country's south.
Netanyahu vows to 'do everything' to restore security in north
Israeli Prime Minister Benjamin Netanyahu has said that his country will "do everything" to defend itself and ensure the security of residents in northern Israel.
His comments came after Hezbollah launched a flurry of rockets and drones at Israel in response to the killing of a senior commander last month.
"We are determined to do everything possible to defend our country, to return the residents of the north safely to their homes and to continue to uphold a simple rule: Whoever harms us — we harm him," Netanyahu said at the start of a Cabinet meeting on Sunday.
He said the military had eliminated "thousands of rockets that were aimed at northern Israel."