"The massacre of the defenceless people in Lebanon once again revealed the ferocity of the Zionist rabid dog to everyone, and proved the short-sighted and stupid policy of the leaders of the usurping regime," Khamenei said in a statement.

He added: "The Zionist regime had failed to learn from its year-long criminal war in Gaza and was now repeating the same mistakes in Lebanon."

Along these lines, he asserted that Iran and its allied groups remain united in support of Hezbollah, stressing that "the fate of this region will be determined by the Resistance forces, with Hezbollah at their forefront."

Iran's First Vice President Mohammad Reza Aref said Saturday that the killing of Hezbollah chief Hassan Nasrallah in an air strike in the Lebanese capital will bring about Israel's "destruction".

"We warn the leaders of the occupying regime that the unjust bloodshed... especially of Hezbollah's secretary general, martyr Seyyed Hassan Nasrallah, will bring about their destruction," Iran's ISNA news agency quoted Aref as saying.

Earlier on Saturday, in a statement, Hezbollah announced the martyrdom of its decades-long leader in an Israeli airstrike on southern Beirut on Friday.

The group hailed Nasrallah's resistance against Israel, vowing to continue his legacy of supporting Palestine and defending Lebanon. 

Lebanon's health ministry gave a preliminary toll of six dead and 91 wounded from the latest strikes on Beirut's densely populated southern suburbs since Friday, the fiercest since Israel's war on Lebanon in 2006.

The health ministry has said hundreds have been killed in Israeli air raids since Monday, the deadliest day of violence since Lebanon's 1975-90 civil war, as Israel's war on Gaza shifted to its northern border.