Iran's supreme leader vowed in a rare address on Friday that his allies around the region would keep fighting Israel, as he defended his country's missile strike on his country's arch-foe.

Ayatollah Ali Khamenei's address in Tehran was the first since Iran launched its second ever attack on Israel and also the first since exchanges of fire pitting Hezbollah fighters against Israeli troops escalated into full-blown war in Lebanon.

Nearly a year after Palestinian militant group Hamas launched the deadliest attack on Israel in its history on October 7, Israel announced it was shifting its focus to securing its border with Lebanon.

Israel says its objective is to allow 60,000 Israelis displaced by a year of cross-border rocket attacks launched by Hezbollah to return to their homes.

Israel's attacks on Hezbollah strongholds around Lebanon have killed more than 1,000 people since September 23, according to the Lebanese health ministry, and forced hundreds of thousands more to flee their homes in a country already mired in economic crisis.

They have also killed a host of Hezbollah commanders, an Iranian general and, in their biggest blow to the group in decades, assassinated its leader, Hassan Nasrallah.

Speaking to a crowd of thousands in Farsi-speaking Iran, he said in Arabic: "The resistance in the region will not back down with these martyrdoms, and will win."

The address comes as Israel weighs retaliation for Iran's missile attack which Tehran said was revenge for the killing of Nasrallah and other top figures.

The escalation has left people in Lebanon fearful that there will be no swift end to the violence engulfing their country. (AFP)