The high level of alert at Israeli missions and institutions around the world will reach its peak this weekend, as Pessah begins and Jews gather across the globe for celebrations. Senior officials said the defense establishment's preparations for a possible Hizbullah attack in response to the February assassination of arch-terrorist Imad Mughniyeh in Damascus would be at its highest over the holiday. The Shin Bet (Israel Security Agency) has in recent weeks completed beefing up security personnel on Israeli civilian aircraft and in Israeli embassies and consulates. Ahead of the holiday, the Counter-Terrorism Bureau in the Prime Minister's Office issued a severe travel advisory warning of an "imminent" attack against Israelis vacationing in Sinai. On Tuesday, Egyptian security officials said they were hunting a number of terror cells in Sinai that were planning to attack a tourist site. Reportedly, gunmen atop four pick-up trucks plan to attack a tourist resort. "The warnings need to be taken seriously, since the threats against Israeli tourists in Sinai are real and serious," Defense Minister Ehud Barak said Tuesday in Sderot, where he laid the cornerstone for a new Elbit Systems factory. In the afternoon, Barak decided to impose a full closure on the West Bank starting Friday night and lasting until after Pessah on Sunday, April 27. According to the travel advisory, recent intelligence has revealed plans by terrorists to target Israelis - 10,000 of whom are expected to travel there - on the Sinai beaches during Pessah. Travelers who have yet to cross the border are encouraged to cancel their plans, and those currently in Egypt are advised to return to Israel immediately. Israel's fears are not limited to Egypt, and senior defense officials said Tuesday that it was possible that Hizbullah was receiving assistance from al-Qaida or global jihad elements around the world in planning and implementing a retaliatory attack. Hizbullah is known to have infrastructure, including sleeper cells, overseas - particularly in Africa and South America - which could be utilized in an attack against an Israeli or Jewish target. Israel is also concerned that Iran or Syria might provide logistical support for an attack. According to intelligence information, the Iranian Revolutionary Guards maintain at least 50 "branches" around the world, but none as active as the one in Lebanon, which works closely with Hizbullah. The Shin Bet and the Mossad are concerned that large gatherings of tourists, as well as public Pessah Seders like those held by Chabad in a number of countries, could be prime targets for Hizbullah terrorists. "Hizbullah can get assistance from a number of dangerous elements abroad, including Syria, Iran and global jihad," a senior defense official said. To counter the threat, the Shin Bet, Mossad and Military Intelligence have set up a team of analysts and security experts to continuously assess the threat level. The team is responsible for analyzing intelligence information collected by the different agencies and for categorizing countries around the world according to threat level and based on assessments of where Hizbullah would likely strike. "There is no place in the world where Israeli security has not been increased," a defense official said. "Everyone is on special Mughniyeh alert."