Imad Mugniyah, 45, died in a car bomb in Damascus, Syria, on Tuesday night. He was believed to have been behind attacks in 1983 on the United States Embassy and Marine barracks in Beirut, the terrorist hijacking of a T.W.A. jetliner in 1985, and a series of high-profile kidnappings in the 1980’s. There have also been accusations that his organization may have been involved in the bombing of the Khobar Towers military residence in Saudi Arabia in 1996, in which 17 Americans were killed.

Hezbollah’s announcement, which blamed Israel for the killing, did not say how Mr. Mugniyah died. But it came just hours after the car bombing in Damascus late Tuesday, in which eyewitnesses said a passer-by was killed. The bomb was placed under a parked car, which was destroyed, and damaged at least 10 others. Syrian security officials quickly towed away the wreckage of the destroyed car and sealed off the area. There was no reference to the bombing in the Syrian media on Wednesday. However, an Iranian satellite channel, Press TV, said on Wednesday that the person killed in the Syrian bombing was believed to be Mr. Mugniyah.

“With pride and honor we announce that a great Jihadi leader has joined the procession of martyrs in the Islamic resistance," said a statement read on Hezbollah’s Al Manar television station. "The martyr was killed at the hands of the Israeli Zionists."

Israel officially distanced itself from the killing and, without specifically naming Mr. Mugniyah, said that it was looking into the attack in Syria. But some former Israeli security officials did not hide their satisfaction at Mr. Mugniyah’s assassination. Danny Yatom, a Labor parliamentarian and former chief of Israel’s Mossad intelligence agency, called Mr. Mugniyah’s death "a great achievement for the free world in its fight on terror."

Shortly after Hezbollah announced his death, mourners poured into Moujamaa al-Shouhada, a Hezbollah stronghold in the southern suburbs of Beirut. In Tary Dibba in south Lebanon, where Mr. Mugniyah was born to peasant parents, black flags were raised and stores were closed.

Hezbollah announced Thursday would be a day of mourning in some parts of south Lebanon, and a mass funeral in the southern suburbs was scheduled for Thursday.

Mr. Mugniyah, who was also known as Mr. Hajj, was one of the world’s most wanted men, with at one point an American price tag on his head of $25 million. He was charged with the hijacking of the T.W.A. jetliner in 1985 and implicated among other things in shipments of arms from Iran to the Palestinians.

American officials assert that Mr. Mugniyah was behind the bombings in Beirut in 1983. A car bomb at the American embassy in April that year killed 63 people, including 17 Americans, while a truck bomb in October at a Marine compound killed 241 American troops.

The United States also assert he was behind the torture and murder of William Buckley, the C.I.A. station chief in Beirut, in 1984; the kidnapping and murder of Lt. Col. William Richard Higgins of the Marines, who was on peacekeeping duty in Lebanon in 1988; and, through the Islamic Jihad Organization, the seizure of Western hostages in Beirut during the 1980s.

In a statement, the office of Prime Minister Ehud Olmert of Israel said: “Israel rejects the attempt by terrorist elements to ascribe to it any involvement whatsoever in this incident.”

Gideon Ezra, a minister from Israel’s governing Kadima Party and former deputy chief of the Shin Bet internal intelligence agency, told Israel Radio Wednesday that many countries had an interest in killing Mr. Mugniyah but that “Israel too was hurt by him, more than other countries in recent years."

Mr. Ezra said, "Of course I don’t know who killed him, but whoever did should be congratulated."

According to witnesses, the bombing of the car took place just after 10:30 p.m. on Monday in Tantheem Kafer Souseh, an upscale neighborhood of Damascus, close to an Iranian school and a police station.

The targeted car, believed to be a black SUV, was badly damaged in the attack “like a shredded metal can,” according to Housham Nasaiseh, 19, who works in a sweetshop nearby, and who arrived at the scene a few minutes after the explosion.

By this morning, the car had been towed away, the scene had been cleared, and the only signs of the attack were a black mark on the ground and damage to nearby buildings.

As well as being described as an arch-terrorist with strong links to Iran, Mr. Mugniyah was believed in Israel to be a master of disguises who may have undergone several rounds of plastic surgery in order to evade capture.

In the Khobar Towers bombing in Saudi Arabia in 1996, the United States has charged that a group known as Saudi Hezbollah, with backing from Iranian officials, was behind the truck bomb. But one American intelligence report says that Talal Hamiyah, a senior lieutenant under Mr. Mugniyah, was involved in the Saudi Hezbollah group during the 1990s.

In May 1996, the lieutenant to Mr. Mugniyah told a colleague that the Islamic Jihad Organization, an offshoot of Hezbollah controlled by Mr. Mugniyah, was prepared to carry out terrorist operations before that year’s election in Israel, but had been directed not to do so by Iran.

Mr. Mugniyah is also wanted for the hijacking in June 1985 of the T.W.A. flight. During the hijacking, an American was killed and 39 Americans were held hostage for 17 days. It is the only terrorist action for which he has been indicted in the United States.

Hamas, the militant Islamic group that controls Gaza, joined Hezbollah in blaming Israel for Mr. Mugniyah’s death, calling it a "new example of Zionist gangster-ism."

A Hamas spokesman in Gaza, Sami Abu Zuhri, called on the Muslim and Arab world to unite against what it called the "Zionist octopus that threatens the security of Arab and Muslim countries."

In 2002, Central Intelligence Agency documents showed Mr. Mugniyah had been operating for years with the protection and backing of the Iranian intelligence services.

American intelligence officials have said that they had sometimes received credible tips about Mr. Mugniyah’s presence in Beirut, but the United States had never attempted to bomb his hideouts or to capture him, according to former American intelligence officials.

In one instance, in the early 1990s, the United States found that Mr. Mugniyah was on a commercial flight that stopped in Saudi Arabia, but Saudi officials refused to arrest him and allowed him to leave the country, they said.

The statement from the Israeli government said that "Israel is looking into the reports from Lebanon and Syria regarding the death of a senior Hezbollah figure and is studying the details" as they were being reported in the news media.

Political scientists speculated why Hezbollah had not confirmed that Mr. Mugniyah had died in Syria. “Hezbollah at least for now believe that Syria has no involvement in his killing,” said Talal Atrissi, a professor of political sciences at the Lebanese University. “That’s why they did not refer to the Damascus bombing in their statement.”

But observers and officials in Beirut speculated that Syria might have a role in his killing as part of a possible deal with the Americans and the Israelis.

“Intelligence agencies exchange favors,” said a Lebanese security official speaking on condition of anonymity because he was not authorized to speak with the media. “They bargain and trade.”