In his first speech since war broke out last month between Hamas militants and Israel, the head of the powerful Lebanese Shiite movement said the United States was responsible for the Gaza war and that Washington could prevent a regional conflagration by halting attacks on the Palestinian territory.

"America is entirely responsible for the ongoing war on Gaza and its people, and Israel is simply a tool of execution," Nasrallah said in a televised broadcast, calling the conflict "decisive".

"Whoever wants to prevent a regional war -- and this is addressed to the Americans -- must quickly stop the aggression on Gaza," he said.

The United States "impedes a ceasefire and the end of the aggression", he added.

During the highly anticipated speech, broadcast as part of an event in Beirut's southern suburbs, a Hezbollah stronghold, Nasrallah warned Israel against attacking Lebanon, saying that "all options are open on our Lebanese front".

"Your fleet in the Mediterranean do not scare us... we are ready to face the fleet you threaten us with," Nasrallah said, also addressing the United States.

Since Hamas militants launched an unprecedented October 7 attack on Israel from the Gaza Strip, Lebanon's southern border has seen escalating tit-for-tat exchanges, mainly between Israel and Hezbollah, an ally of the Palestinian group, stoking fears of a broader conflagration.

The cross-border skirmishes have killed 72 people on the Lebanese side, among them at least 54 Hezbollah fighters but also other combatants and civilians, one a Reuters journalist, according to an AFP tally.

On the Israeli side, at least six soldiers and one civilian have been killed, the army said.

Nasrallah said his group had "entered the battle on October 8" and warned that the chance of open conflict was "realistic".

"We say to the enemy that might think of attacking Lebanon or carrying out a pre-emptive operation, that this would be the greatest foolishness of its existence," he said.