Iran's supreme leader, Ayatollah Ali Khamenei , has gone into hiding and remains in a safe place inside the country, sources told Reuters.
The decision came in response to Israeli strikes outside Beirut on Friday that killed the leader and founding member of the Iran-backed Hezbollah terror group, Hassan Nasrallah.
Two sources also told Reuters that Iran contacted Hezbollah and other proxy forces in the region to determine what action to take in response to Nasrallah's killing.
In a statement on Saturday, Khamenei said: " The fate of this region will be determined by the resistance forces, with Hezbollah at the forefront ."
As he declared five days of public mourning, Khamenei called Nasrallah " the flag bearer of the resistance " in the region.
"The blood of the martyr will not go unavenged," Khamenei said, according to Reuters.
Iranian media reported on Saturday that Israeli strikes outside the Lebanese capital also killed the deputy commander of Iran's Revolutionary Guard, Abbas Nilforoushan .
Israel has killed several other top Hezbollah commanders in Beirut, particularly in the past two weeks, in addition to the attack that killed Nasrallah.