The twin killings have sent Middle East tensions skyrocketing, amid fears of a regional conflict and all-out war between Israel and Hezbollah, which have been trading daily cross-border fire since Israel’s war on Gaza began in October.

Iran "finds itself obliged to respond, and the enemy is waiting in a great state of dread", Hassan Nasrallah said in a televised address, adding his group was also "obliged to respond".

Hezbollah will retaliate "alone or in the context of a unified response from all the axis" of Iran-allied groups in the region, "whatever the consequences," he added.

"Hezbollah will respond, Iran will respond, Yemen will respond, and the enemy waits, watches and evaluates each reaction. The main thing is that the determination, the decision and the capability are there," Nasrallah asserted.

An Israeli air strike on Beirut's southern suburbs killed Hezbollah's top military commander Shukr last Tuesday.

Early Wednesday, Hamas's political chief Haniyeh was killed in an attack in Tehran widely blamed on Israel, which has not commented directly on the killing.

"Our response is coming," Nasrallah said in an address to mark a week since Shukr's killing, adding it would be "strong and effective".

"Israel's waiting for a week is part of the punishment, part of the response, part of the battle," he said, adding: "It is Israel who chose escalation... and who attacked Iran."

*This story was edited by Ahram Online.