BEIRUT: Lebanese Hezbollah’s head Hassan Nasrallah vowed on Thursday to respond to Israel’s killing of the group’s top military commander, saying its decades-old foe had “crossed red lines.”

An Israeli strike on Hezbollah’s stronghold in the southern suburb of Beirut on Tuesday killed top commander Fuad Shukr, along with an Iranian military advisor and five civilians.

It was the most serious blow to the Iran-backed group in nearly two decades and threatened to push the tit-for-tat exchanges across Lebanon’s southern border in parallel with the Gaza War into a full-blown regional conflict.

Speaking in a televised address to mark the funeral of the slain commander, Nasrallah said the conflict had entered “a new phase unlike the previous one” and that Israel had crossed red lines with its attack on the group’s stronghold.

Hezbollah to hit new areas in Israel if it keeps targeting civilians, Nasrallah says

Nasrallah said unnamed countries had asked his group to retaliate in an “acceptable” way - or not at all. But he said it would be “impossible” for the group not to respond.

“There is no discussion on this point. The only things lying between us and you are the days, the nights and the battlefield,” Nasrallah added in a threat to Israel.

He said the group had ratcheted down its operations over the last two days out of respect for the victims of the strike but would “go back to work normally starting tomorrow morning,” although the retaliation for Shukr’s killing would come later.

“The response will come, whether spread out or simultaneously,” he said.

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Just hours after Shukr’s killing, the leader of Hamas Ismail Haniyeh was killed in the Iranian capital Tehran in an attack widely blamed on Israel.

Nasrallah said that anyone seeking to prevent the region from slipping into a tailspin should work on a Gaza ceasefire.

“There will be no solution here except to stop the aggression on Gaza,” he said.