Israel ordered its military and embassies to go on alert Thursday, and advised Jewish institutions worldwide to follow suit, as Lebanese guerrillas threatened to avenge the assassination of a fugitive commander tied to a string of spectacular attacks against U.S. and Jewish targets.

Israel's government swiftly denied involvement in the death of Imad Mughniyeh, killed in a car bombing Tuesday in the Syrian capital of Damascus, although military officials were more vague, refusing to confirm or deny involvement.

Israel's interest in seeing Mughniyeh dead left his Hezbollah militia, its Iranian backers and others pointing a finger at the Jewish state. On Thursday, Hezbollah's chief vowed to retaliate against Israeli targets abroad, and Israel beefed up its troop presence along the Lebanese border.

One of the world's most wanted and elusive terrorists, the 45-year-old Mughniyeh was the suspected mastermind of attacks that killed hundreds of Americans, including 241 U.S. Marines, in Lebanon and the brutal kidnappings of Westerners in the 1980s.

His trail of terror was believed to have extended into the 1990s, with the bombing of the Israeli Embassy in Argentina, a Jewish center in Buenos Aires and an attack on foreign military housing in Saudi Arabia. Dozens died in those attacks.

In Israel, military chief Lt. Gen. Gabi Ashkenazi put forces on heightened alert, instructing them to "take the necessary precautions by air, land and sea in order to protect the northern border and other Israeli interests," the army said.

The military sent more troops to the already heavily patrolled northern border with Lebanon, defense officials said, without elaborating. And soldiers were ordered to be on guard for attacks and kidnappings on both the border with Lebanon and in the Palestinian territories.

Israeli embassies worldwide also were put on alert, and Israeli security advised Jewish institutions across the globe to be vigilant, Israeli officials said on condition of anonymity because they were not authorized to discuss security matters with the press. Israel's Foreign Ministry would not comment.

Israel Radio reported that security had been raised on airplanes and ships and at sensitive installations.

In a statement from the Prime Minister's Office, the Israeli anti-terror command center warned Israelis to act with extra caution when they are abroad, noting the threat of kidnapping. It listed staying out of Arab and Muslim countries, avoiding concentrations of other Israelis and turning down "unexpected invitations to meetings in remote places."

"There is no doubt Hezbollah and its Iranian masters, who had excellent relations with Mughniyeh, have long memories and will demand revenge," military analyst Yossi Melman wrote in the Haaretz newspaper. "It will not necessarily come immediately in a reflex action."

Israel fought a fierce but inconclusive, monthlong war with Hezbollah in the summer of 2006, and residents of northern Israel were afraid a new war was on its way.

"Everything can get all messy after one incident like this," said Shuli Oozan, a 47-year-old convenience store employee in the town of Shlomi near the Lebanese border. The town was a frequent target of Hezbollah rocket attacks during the war, and was hit by two rockets fired last month, apparently by a smaller Lebanese group.

The rockets killed 40 Israeli civilians. The war also claimed the lives of 119 Israeli soldiers and more than 1,000 Lebanese, most of them civilians.

But while Israelis worried about the possibility of renewed war on their turf, Hezbollah chief Sheik Hassan Nasrallah declared on Thursday that his guerrilla group would hit Israeli targets abroad.

"You have killed Hajj Imad outside the natural battlefield," Nasrallah said in a fiery eulogy, referring to Hezbollah's contention it only fights Israel within Lebanon and along their common border.

"Zionists, if you want this kind of open war, let the whole world listen: Let this war be open," Nasrallah said in a videotaped message broadcast at the ceremony.

Even before Nasrallah broke his silence on the killing, Israeli analysts doubted Hezbollah would try to exact revenge with a new round of cross-border hostilities.

Hezbollah bombarded northern Israel with nearly 4,000 Katyusha rockets during the fighting, but Israel destroyed some of Hezbollah's arsenal of rockets and contends it killed hundreds of Hezbollah fighters, a claim the group denies.

Hezbollah sparked the war by killing three Israeli soldiers and capturing two others in a cross-border raid, and Nasrallah has said he would not have ordered the soldiers seized if he knew Israel would respond so severely.

Nasrallah went into hiding in 2006, fearing an Israeli assassination. He has made only three public appearances since the war.

"Hezbollah doesn't want to heat up the border," said Ephraim Kam, an Israel-based Iran analyst. "It's afraid Israel would strike it again hard, and Israel is better prepared to fight now, having learned the lessons of the war."

The likelier avenue "would be a spectacular terror attack, not necessarily against Israel itself," but something like the embassy attack in Argentina, Kam said.

"It won't necessarily take place tomorrow morning," he added. "It takes time to carry out a spectacular attack."

Yaakov Perry, a former chief of Israel's internal security service, said Hezbollah might act against Israel through allied Palestinian militant groups.

"Hezbollah doesn't usually act alone, but acts with others, the best-known being Hamas and Islamic Jihad. Those who live among us, alongside us, could be its long arm."

After word of the assassination got out, a Hamas spokesman in Gaza, Sami Abu Zuhri, appealed to the Muslim world to "rise up to confront the Zionist devil, which is backed by the Americans."

Although Israeli denied any involvement, officials made no effort to conceal their satisfaction he was dead. Israel blamed Mughniyeh for the 1992 bombing of its embassy in Buenos Aires, Argentina, in which 29 people were killed. Argentina linked him to the 1994 bombing of a Buenos Aires Jewish center that killed 85 people.

Despite its denials, Israel is widely believed to have carried out daring, complex and deadly strikes against other terror masterminds, sometimes deep in enemy territory.

Palestinian Liberation Organization official Khalil Al-Wazir, linked to attacks that killed dozens of Israelis, was assassinated at close range in his home in Tunis in 1988, reportedly by an Israeli commando team ferried from Israel by boat, and aided ashore by Mossad intelligence agency operatives. Islamic Jihad leader Fathi Shkaki was gunned down in Malta in 1995 by a man on a motorcycle. In 2004, a senior Hamas militant was killed in a car bombing in Damascus.

Israeli commentator Ben Caspit said the Mughniyeh assassination was a double-edged sword for Israel.

It was "good, because Mughniyeh was thirsty for Jewish blood wherever it was," Caspit wrote. It was bad, "because after Mughniyeh will come a new Mughniyeh, as always happens, and revenge will also come, as it always does."