Israel is on high alert, said Prime Minister Benjamin Netanyahu Thursday afternoon after Iran and its ally Hezbollah threatened to retaliate for the killing of senior leaders of Hezbollah and Hamas this week.

"Israel is highly prepared for any scenario, both defensively and offensively," Netanyahu said in a video released by his office during a visit to a Home Front Command base.

"We will exact a very heavy price for any act of aggression against us from any arena," he added. 

An Israeli strike in the southern suburb of Beirut on Tuesday killed Fouad Shukur, head of Hezbollah's military operations, along with an Iranian military adviser and five civilians.

Just hours after Shukur's killing, the political leader of Hamas, Ismail Haniyeh, was killed in the Iranian capital, Tehran.

Israel has not taken responsibility for Haniyeh's death.