By Dana Karni, Tamar Michaelis, Alex Marquardt and Kathleen Magramo, CNN

Tel Aviv, Israel (CNN) — The Israeli military launched what it called “preemptive” strikes against Hezbollah in Lebanon, as the Iran-backed militant group said it carried out its own attacks in response to the killing of a top commander.

The overnight strikes are some of the most serious yet between Israel and Hezbollah, who have been exchanging fire for months. The hostilities have raised the specter of a regional conflagration, prompting intense diplomatic efforts to de-escalate tensions.

The Israel Defense Forces (IDF) said about 100 of its fighter jets “struck and destroyed thousands of Hezbollah rocket launcher barrels” across dozens of launch sites from Lebanon on Sunday. It followed these up with further attacks later in the day.

Israel said it carried out the strikes in self-defense after identifying that Hezbollah was “preparing to fire missiles and rockets toward Israeli territory.” Hezbollah called Israel’s description of its strike as preemptive “baseless.”

“We removed a wider threat, probably also a future threat in some areas,” IDF spokesperson Rear Admiral Daniel Hagari said Sunday.

Soon after the Israeli raids, the IDF said approximately 200 rockets had been launched from Lebanon towards Israel early Sunday, with no reports of injuries so far. Hezbollah said the “first phase” of its strikes against Israel “ended with complete success,” claiming that it launched 320 rockets and a barrage of drones toward Israel.

Hezbollah said it carried out strikes towards Israel in response to the killing of top military commander Fu’ad Shukr last month in the southern suburbs of Beirut, a populous neighborhood that is also the Iran-backed group’s stronghold.

Israeli Prime Minister Benjamin Netanyahu said the military intercepted “all of the drones that Hezbollah launched to a strategic target in the center of the country,” Netnyahu said, without clarify what the target was.

Netanyahu added that “what happened today is not the end,” and that Hezbollah leader Hassan Nasrallah in Beirut and Iranian Supreme Leader Ali Khamenei in Tehran “should know that this was another step on our way to change the situation in the north and safely return our residents to their homes.”

One Israeli soldier, 21-year-old David Moshe Ben Shitrit of the Israeli Navy, was killed in the fighting. He and two others were injured “either directly from an Iron Dome interceptor or from falling shrapnel from the interceptor that accidentally hit a Dvora-class fast patrol boat after intercepting a UAV,” an army official told CNN.

Two people were killed in Israeli strikes on the village of At Tiri in Nabatiyeh in southern Lebanon, Lebanese health officals said, and a third was killed when a car was hit in the town of Khiyam. The Hezbollah-allied Shia group Amal movement also said one of its fighters, was killed in Khiyam, but it is unclear if they are the same person.

For the Lebanese group, Shukr’s assassination was a change in the rules of engagement, Danny Citrinowicz, research fellow in the Iran Program at the Institute for National Security Studies (INSS) in Tel Aviv, said. “They had to retaliate,” Citrinowicz told CNN, adding that the group may have been trying to “draw a line in the sand” to avoid further attacks.

“The question was not if but when,” he said, adding that it is yet to be seen whether the group will be content with its attack or whether more projectiles will follow in the coming days.

Ceasefire talks resume despite strikes

The attacks took place just hours before mediation talks resumed in the Egyptian capital Cairo, which aim to strike a ceasefire-hostage deal between Israel and Hamas.

An Israeli official told CNN on Sunday afternoon that Israeli negotiators arrived in Cairo for ceasefire and hostage release negotiations.

“I don’t think Iran wants to find itself in escalation, especially when the US presence in the region is (now) in staggering numbers,” he said, adding this is indicative of de-escalatory efforts.

The Iranian government is yet to react to the cross-border fire between Israel and Hezbollah, something Citrinowicz said suggested Iran was willing to distance itself from Hezbollah’s attack amid the negotiations in Cairo.

Following the strikes, Israeli Minister of Defense Yoav Gallant declared a “‘special situation on the home front’ across the country,” which enables the Israeli military to issue instructions to citizens, “including limiting gatherings and closing sites where it may be relevant.”

US President Joe Biden is closely monitoring events in Israel and Lebanon, the White House said Saturday night.

Rocket fire toward Israel by Hezbollah militants in southern Lebanon has become a near-daily occurrence since the outbreak of war in Gaza, but there has been an increasing number of skirmishes.

On Friday, Hezbollah had claimed 15 strikes against Israel. Hezbollah also acknowledged the death of seven fighters on Friday but did not specify where or when they were killed. The IDF said a total of 110 projectiles were launched from Lebanon towards Israel on Friday, marking one of the fiercest days of cross-border fire in recent weeks.

Flights have resumed at Tel Aviv airport after being temporarily suspended for less than two hours on Sunday. A brief restriction on gatherings in northern Israel has also lifted, except for the immediate border area with Lebanon and some settlements in the Israeli-occupied Golan Heights.