"Israel is at a very high level of preparation for any scenario, both defensive and offensive. We will make any act of aggression against us pay a very high price," Netanyahu said in a statement.

"Those who attack us, we will attack in return."

His comments came as Hezbollah chief Hassan Nasrallah warned Thursday that the Lebanese armed group was bound to respond to Israel's killing of its top military commander, Fuad Shukr, in a strike on Tuesday in a Beirut suburb.

On Wednesday, Hamas chief Ismail Haniyeh was killed in a strike in Tehran, which Iran and Hamas have blamed on Israel. Israel has declined to comment on his killing.

"You do not know what red lines you crossed," Nasrallah said addressing Israel during a speech broadcast at Shukr's funeral.

"The enemy, and those who are behind the enemy, must await our inevitable response."