Hezbollah's chief said Tuesday his group and Iran were "obliged to respond" to Israel "whatever the consequences" after the killings last week of Hezbollah military commander Fuad Shukr and Hamas leader Ismail Haniyeh.
The twin killings have sent Middle East tensions skyrocketing, amid fears of a regional conflict and all-out war between Israel and Hezbollah, which have been trading daily cross-border fire since Palestinian militant group Hamas's October 7 attack on Israel.
Iran "finds itself obliged to respond, and the enemy is waiting in a great state of dread", Hassan Nasrallah said in a televised address, adding his group was also "obliged to respond".
Hezbollah will retaliate "alone or in the context of a unified response from all the axis" of Iran-backed groups in the region, "whatever the consequences," he added.
"Today, the region is facing real dangers," he said.
An Israeli air strike on Beirut's southern suburbs killed Hezbollah's top military commander Shukr last Tuesday, along with an Iranian military adviser and five civilians.
Early Wednesday, Hamas's political chief Haniyeh was killed in an attack in Tehran blamed on Israel, which has not commented directly on the killing.
"Our response is coming," Nasrallah said in an address to mark a week since Shukr's killing, adding it would be "strong and effective".
"Israel's waiting for a week is part of the punishment, part of the response, part of the battle," he said, adding: "It is Israel who chose escalation... and who attacked Iran."
"We cannot ask anyone, in Lebanon or outside Lebanon, to treat this attack that happened last Tuesday as a normal attack in the context of the ongoing battle" against Israel, he said.
The United States has said it was working "around the clock" to avert an all-out war in the Middle East.
Washington has sent extra warships and fighter jets to the region in support of Israel, and US President Joe Biden held crisis talks on Monday with his national security team.
"The Americans say to Iran and Lebanon and everyone, 'be patient and give us a little time because we are working to stop the war in Gaza', and they ask us, 'isn't it your goal to stop the Gaza war'?" Nasrallah said.
"Yes, the goal is to stop the aggression on Gaza and the war on the Palestinian people," Nasrallah said.
"But who can trust the Americans after 10 months of deceit and hypocrisy and lying to all the international community and peoples of the world?"
The goal of the battle "is to prevent Israel from winning and from eliminating the Palestinian resistance", he added.