Hezbollah chief Hassan Nasrallah and Iran's Islamic Revolutionary Guard Corps Commander Hossein Salami vowed revenge against Israel on Thursday after two days of blasts targeting fighters from the Lebanese group killed at least 37 people and wounded around 3,000.
The attacks widely blamed on their mutual foe ratchet up already flaring tensions across the Israeli-Lebanese border but appeared to stop short of heralding an imminent regional war.
"There is no doubt that we have been exposed to a major and unprecedented blow on the security and humanitarian levels," Nasrallah told supporters via video link from an undisclosed location.
"It can be called a declaration of war", Nasrallah added, vowing a "severe reckoning and just punishment".
Israel has not yet commented on any role in the back-to-back waves of attacks which hit pagers and walkie-talkies.
In the day before nationwide blasts hit pagers carried by Hezbollah members, Israel on Monday upgraded the aims of its nearly one-year-old war against the group's Palestinian allies Hamas to include returning the 60,000 citizens who have been evacuated from their homes due to Hezbollah fire.
'Complete destruction'
The chief of the Iran's transnational paramilitary organisation the IRGC also predicted on Thursday that the informal alliance of armed Islamist militias Iran leads throughout the region would punish the Jewish state.
"Soon we will witness the complete destruction of this cruel and criminal regime with the crushing response of the resistance front," Hossein Salami told Nasrallah on Thursday, Iranian state media reported.
Salami also visited Iran's ambassador to Lebanon in a Tehran hospital on Thursday where the envoy was taken after being stricken by the original blasts, in injuries the New York Times quoted IRGC sources as saying left him blind in one eye.
No retaliation yet
Since the assassination of Hamas leader Ismail Haniyeh in Tehran on July 31 - an attack Iranian officials attribute to Israel - Tehran has pledged retaliation but has yet to land any blow.
Iran launched a large-scale missile and drone strike on Israel in April following a deadly Israeli attack on Iran's consular compound in Damascus.
US Secretary of State Antony Blinken on Thursday warned against escalation in the Middle East, after the US said it conveyed to Iran through back channels that it had no foreknowledge or hand in the attacks.
“We don’t want to see any escalatory actions by any party," Blinken said in remarks on a visit to Paris.
Hezbollah has long been Iran’s strongest ally in Lebanon and a central figure in its broader regional strategy.
The group was founded in the 1980s with direct Iranian assistance via the IRGC to fight Israeli forces in southern Lebanon. Since then, Hezbollah has grown into both a political force in Lebanon and a powerful militia that frequently engages in conflict with Israel.