Israel put its embassies and Jewish groups around the world on alert Thursday after Hezbollah accused the nation of assassinating its top guerrilla commander and declared "open war" on the country.

"Zionists, if you want this kind of open war, let the whole world listen: Let this war be open," Hezbollah leader Hassan Nasrallah said via video during an appearance at the funeral for Imad Moughniyeh in Beirut.

"At your orders, Nasrallah," thousands of supporters shouted back to the man many claim defeated Israel during a brief war in 2006.

Mughniyeh -- one of the world's most wanted for decades and the former security chief of Hezbollah -- was killed Tuesday night in a car bombing in Damascus, Syria.

A picture of Mughniyeh that was released after his death was one of the first images seen in years. It showed he had gained weight and apparently undergone some facial reconstruction to alter his appearance.

"It says a lot about exactly how . . . wanted he was and exactly what a mastermind he was, that he was able to avoid authorities for so long," Janis Mackey Frayer, CTV's Middle East bureau chief, reported Friday.

Israel and the U.S. have both denied any involvement in Mughniyeh's death, but have not expressed any regrets about it.

"Israel is definitely sensing some satisfaction with this. They're denying they had any involvement with the assassination of Mughniyeh but they are welcoming it, as (is) the United States," Mackey Frayer said.

In the U.S., the domestic terror squads for the FBI were put on alert, watching specifically for threats against synagogues or Jewish centers.

Hezbollah and Iran have both blamed Israel for the bombing that blew up Mughniyeh's SUV in Damascus.

Meanwhile, supporters of the Western-backed government crowded a downtown square to mark the assassination of former Prime Minister Rafik Hariri in 2005.

That put Hariri's and Mughniyeh's opposing groups in close proximity -- creating a potential powder keg.

Heavy rain and a strong military presence may have helped prevent serious conflict.

"It's always a formula for tension and certainly that was seen across Beirut. Thousands of army troops as early as yesterday started blocking off streets. There are still (troop carriers) parked on street corners here as a means to keep the factions apart," Mackey Frayer said.

Leaders on both sides had appealed for calm as it became evident they would be marking major events on the same day and in the same city.