Hezbollah chief Hassan Nasrallah warned Thursday that the group was bound to respond to Israel's killing of its top military commander, saying his death and that of the Hamas leader "crossed" red lines.

"The enemy, and those who are behind the enemy, must await our inevitable response," he said in a speech broadcast at the funeral of Hezbollah military commander Fuad Shukr.

"You do not know what red lines you crossed," he said, addressing Israel after separate strikes in Beirut and Tehran killed Shukr and Hamas political leader Ismail Haniyeh. 

Israel has not commented on Haniyeh's killing, but it announced that it had "eliminated" Shukr, describing him as Hezbollah's "most senior military commander" and Nasrallah's "right-hand man".

Shukr, who used the nom de guerre Hajj Mohsen, led operations in south Lebanon, where the group says it has opened a "support front", exchanging near-daily fire with Israel since war erupted in Gaza in October.

"We, on all the support fronts, have entered a new phase," Nasrallah said, referring to Hezbollah and other Iran-backed groups that have targeted Israel in support of Hamas after the Palestinian group launched an October 7 attack on Israel.