Hizbullah secretary general Hassan Nasrallah threatened strikes on Israeli targets across the globe after the assassination in Syria of one of his top military commanders, raising the prospect of an "open war".
"You have crossed the borders with this murder, its timing, its location and method. Zionists, if you want this kind of open war, let the whole world hear: Let it be an open war," Sheikh Nasrallah told tens of thousands of supporters gathered to mourn Imad Mugnieh, who was killed by a car bomb in Damascus on Tuesday night.
"Mugnieh's blood will lead to the elimination of Israel. These words are not an emotional reaction," Sheikh Nasrallah told the crowds.
After the funeral ended, supporters fired shots in the air in the southern suburbs and Shia areas of central Beirut.
Israel denies any involvement in Mugnieh's assassination, but welcomed his death. Following Sheikh Nasrallah's threat, it put its military and embassies on high alert and advised Jewish institutions to do likewise.
Soldiers were ordered to be on guard for attacks and kidnap attempts on Israel's borders with the occupied Palestinian territories and Lebanon. But observers in Beirut thought a border attack unlikely so soon after the destructive July 2006 war, which followed Hizbullah's kidnapping of two soldiers.
All agreed Sheikh Nasrallah's words marked a turning point. "What Nasrallah and Hizbullah are saying is that the rules of the conflict have radically changed now and that Hizbullah reserves the right to do exactly the same and break the rules of the game and take it outside the old theatre of conflict to a global stage," said Nicholas Noe, Beirut-based editor of a book of the sheikh's speeches.
Mr Noe said that raised the prospect of Hizbullah, which has become a mainstream, if controversial, political force in Lebanon, returning to the tactics of its more radical days in the 1980s.
Mugnieh was on the FBI's most-wanted terrorist list, accused of masterminding the kidnappings of western hostages during the Lebanese civil war of 1975-1990 and the 1983 bombings of US marine barracks and a French peacekeeping base in Beirut. More than 300 people were killed in these attacks. Washington welcomed his death.
Few hard facts are known about Mugnieh - before announcing his death, Hizbullah rarely acknowledged the existence of an almost mythical man who lived for decades under cover between Iran, Syria and Lebanon. But he is widely seen as one of its most senior military commanders and strategists.
As a sign of Mugnieh's importance, Manouchehr Mottaki, the foreign minister of Hizbullah's main backer Iran, attended the funeral, held inside a hangar-sized meeting hall.
Following prayers, tens of thousands of black-clad mourners, also under a sea of umbrellas, followed Mugnieh's coffin, draped in Hizbullah's yellow flag and surrounded by the group's security personnel in green berets.