When the matter was reported to Israeli security, El Al changed the flight paths of all its Geneva-bound planes, landing them at Zurich Airport the following week.

Swiss officials reported that no arrests were made following the discovery since the plan had yet to reach its final operational stages.

El Al has reportedly installed the Flight Guard Self Protection System at a cost of one million dollars per plane on some of its fleet, and plans to install it in all its jets in the future.

However, the system, which is capable of detecting an approaching missile, would be largely useless against an 'unguided' weapon such as the RPG, which is not radar-guided and does not expel enough heat to be tracked.

If confirmed as a targeted attack, it would mark the highest-profile internal assassination attempt in the
West Bank and Gaza Strip and could worsen enflamed tensions between loyalists of Abbas's Fatah group and Hamas supporters.

The Hamas-led government, formed after the Islamic militant group beat Fatah in a January parliamentary election and which is shunned by Washington and other world powers because of its vow to destroy Israel, said an investigation would be launched.

Saturday's missile strike, which medics said also killed a boy and his mother and grandmother, was the latest such attack since April, when an Israeli air strike killed an Islamic Jihad militant after a deadly suicide bombing by the group in Israel.

The militant, Mohammad al-Dahdouh, was a senior Islamic Jihad commander responsible for recent firings of advanced Russian-made rockets into Israel, a spokesman for the group and the Israeli army said.

Islamic Jihad has masterminded dozens of anti-Israeli attacks since a Palestinian uprising began in 2000 and killed 11 people in the Jewish state last month in a suicide bombing.

"The Zionist enemy should hurry to evacuate the settlers from (the Israeli city of) Ashkelon because our developed rockets ... will hunt them day and night," said Islamic Jihad spokesman Abu Ahmed.

GAZA INTERNAL VIOLENCE

Clashes erupted in Gaza earlier between Fatah and Hamas supporters after the blast at Abu Rajab's headquarters.

He was taking an elevator surrounded by a phalanx of bodyguards and aides when it exploded, apparently when a bomb planted in the lift shaft was detonated, security sources said.

He was taken at Abbas's request to an Israeli hospital, where a spokeswoman said he sustained many intense injuries and was on a respirator. Palestinians have often been brought to Israel for medical treatment due to better equipment.

Tensions between Hamas and Fatah have mounted since the militant group, which is sworn to Israel's destruction, won the election and flared after Hamas formed a new 3,000-member security force last month to counter officers loyal to Abbas.

"Incitement will lead to an explosion and to more serious incidents," Palestinian Deputy Intelligence Chief Tawfiq Tirawi said in the West Bank city of Ramallah. "What happens in Gaza may be transferred to the West Bank at any minute."

After the blast, gunmen from the rival groups clashed in a gunfight, which wounded a boy. Dozens of members of the family of Rajab's aide and Fatah supporters protested against the new Hamas force, chanting, "Fatah, Fatah!" and burning tires.

Tirawi told reporters that the Hamas forces may have caused the explosion. The Palestinian Interior Ministry said it would launch an investigation into the incident, which Hamas spokesman Sami Abu Zuhri called "unfortunate."

Tirawi said the Hamas "militias" have recently been buying and collecting weapons and explosives. Several Palestinian officials said Hamas has been purchasing arms in the West Bank and Gaza since it won a parliamentary election in January.

There was no immediate comment from Hamas.

Palestinian security sources had said in recent days that they had suspected an assassination plot against Abu Rajab was in the works. Masked gunmen had shot and wounded one of the intelligence chief's bodyguards on Sunday.

Hamas was accused of being behind a 2004 assassination attempt against Abu Rajab in which he was shot by unidentified gunmen. Hamas has denied responsibility.