Hezbollah chief Hassan Nasrallah pledged to retaliate against Israel for assassinating top commander Fuad Shukr, amid the escalation of tensions as Israel amplifies its attacks across the region.

"Our response is coming," Hassan Nasrallah said during the funeral of Fuad Shukr, the group's top military commander and the head of its operations in southern Lebanon.

He stressed that Israel and those behind it must "inevitably wait for our next response," stressing that "there is no discussion or debate about this," and reiterating that "between us and you are the days, the nights, and the battlefield."

He added that they are looking for "a real response and real opportunity."

Israel's military killed Shukr on Tuesday evening. A few hours later, the leader of the Palestinian resistance movement Hamas, Ismail Haniyeh, was assassinated in an attack in the Iranian capital Tehran.

Since then, there have been fears of a potentially large, coordinated attack on Israel by Iran, Hezbollah and other allies in the region.

"We are in an open battle on all fronts that has entered a new phase," said the Hezbollah secretary-general via a video link message at the Shukr's funeral in Beirut.

Nasrallah said the killing of Haniyeh in Tehran was an "attack on Iran’s honor."

Nasrallah said he had been in constant contact with Shukr, who trained most of Hezbollah's commanders and was a "pillar" of the group, before his death.