Israel was on high alert yesterday after Hezbollah’s leader declared “open war” on the Jewish state, following the assassination of one of its top military commanders.

The alert spread around the world, with fears that the Lebanese militia would target Jewish civilians, institutions and temples abroad. The Government told Israelis living overseas or travelling not to leave their passports in hotel rooms and to avoid large gatherings with fellow citizens.

In Israel police were on alert and extra troops were sent to the northern border with Lebanon to guard against cross-border raids such as the July 2006 Hezbollah ambush that killed three Israeli soldiers and captured two more, triggering a month-long war.

The heightened alert followed a speech by Hassan Nasrallah, the Hezbollah leader, at the funeral of Imad Mughnieh who was killed by a car bomb in Damascus. The Hezbollah chief blamed Israel for the attack and said that his militia would retaliate. Israel denied any role in the killing of Mughnieh, believed to have master-minded a bloody ambush on the Israeli Embassy in Argentina 16 years ago, as well as other attacks on Israeli and American targets.

“The big . . . question arising from the killing in Damascus is not whether Hezbollah will respond, but how and when,” Yossi Melman, an Israeli commentator, wrote in the Haaretz newspaper. Security sources quoted in the paper said that they expected Hezbollah to do something in the “immediate future” followed by a “showcase attack” in the medium term.

An unidentified defence official told the Jerusalem Post that there could be as many as 50 Hezbollah cells put on standby around the world for attacks on Israeli and Jewish targets.

Israel’s counter-terrorist agency urged citizens to “absolutely avoid visiting or staying in Arab/Islamic countries for which travel advisories have been issued, to reject any enticing or unexpected proposals and refuse to accept any unexpected gifts or offers from suspect or unknown sources”.

Stepped-up security measures were also recommended for El Al, the national airline, for shipping and for synagogues and Jewish institutions around the world. Analysts believed that Syria would also respond to the attack on its soil by upping its interference in Lebanon, making further attempts to block pro-Western candidates from gaining control.

Since the 2006 war, Israel has been hit at least twice by Katyusha rockets fired from Lebanon, although they were believed to have been launched by Palestinian militants in refugee camps. There were fears that such attacks could resume, or even a new round of rocket bombardment by the Shia militia itself. And the US State Department gave warning that Hezbollah may order a suicide bombing by Palestinians through groups it funds.

Hezbollah also has strong ties to Hamas, the Islamist movement that seized power in the Gaza Strip and which regularly fires rockets at southern Israel. It may encourage a new round of attacks, with Israeli security analysts giving warning that the group has a growing arsenal of longer-range missiles capable of hitting the southern Israeli city of Ashkelon.

— Last night Ayman Fayed, a senior commander of the Palestinian Islamic Jihad movement, was killed during what was described as an airstrike. Fayed, better known as Abu Abdallah, was among at least five killed and up to 40 wounded when his three-storey home in Gaza was hit by an explosion. An Israeli military spokesman said that he was not aware of any action.

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