PLO second in command Khalil al-Wazir (left) was assassinated by Israeli commandos in TunisiaBy Heather Sharp
BBC News, Jerusalem
The Islamic movement Hamas claims that the death of one its senior commanders, Mahmoud al-Mabhouh, is the latest in Israel's history of assassinating individuals it believes to have been behind attacks on its citizens.
Israel's general policy is to neither confirm nor deny allegations about the activities of its intelligence agents but it is notable that many of its enemies meet suspicious and violent deaths.
"We are witnessing an intense intelligence struggle, most of it is covert, some of it overt," said Ronen Bergman, author of By Any Means Necessary, and other books and articles on Israel's covert operations. Among the best documented of Israel's assassinations were a wave of killings of pro-Palestinian militants in Paris, Nicosia, Beirut and Athens, carried out in response to the hostage crisis at the Munich Olympics in 1972 which resulted in the deaths of 11 Israelis.
Methods used included a booby-trapped telephone, a bomb planted in a bed, and a raid in Beirut in which current Defence Minister Ehud Barak dressed as a woman.
There are even claims that a poisoned chocolate was later used to kill a commander of the Popular Front for the Liberation of Palestine in East Germany in 1978.
In 1987 Israel made no attempt to disguise their assassination of Khalil al-Wazir - known as Abu Jihad - the Palestine Liberation Organisation's military leader and second in command.
Israeli commandos crept into Tunisia, where the PLO's exiled leadership was based, and shot him several times in his own home before escaping by sea.
It was an operation in which Mr Barak is also believed to have been involved.
Covert failure
In 1997 during the current Prime Minister Benjamin Netanyahu's first term in office, one special operation went humiliatingly wrong.Israeli agents tried to kill Khaled Meshaal, who was then a
fund-raiser for Hamas based in Amman.Disguised as Canadian tourists, they injected poison into his ear - but he was rushed to hospital before it took full effect.
Mr Meshaal's life was literally saved by Jordan's then King Hussein, who was outraged by the attack and - boosted by pressure from then US President Bill Clinton - demanded the Israeli government hand over the antidote.
The agents - who had been arrested - were exchanged for an Israeli apology and the release of 20 prisoners, including Sheikh Ahmad Yassin, Hamas's spiritual leader.
Mr Meshaal has gone on to become Hamas's Damascus-based leader.
Targeted killings
As the second Intifada, or Palestinian uprising, raged in the years after 2000, Israel turned its sights on militant leaders within Gaza and the West Bank.Militant groups sent waves of suicide bombers to attack Israeli civilian targets such as buses and cafes.
Part of Israel's response was the controversial policy it described as "targeted" killings - Amnesty International described them as "extra-judicial".
Palestinians say dozens of militant figures, including Sheikh Yassin and another senior Hamas leader Abdel Aziz al-Rantissi, were killed, in many cases by missiles launched from helicopters.
But in 2008, allegations of Israeli action farther afield intensified with the death of Hezbollah commander Imad Mughniyeh, implicated in numerous bomb attacks and a wave of hostage-taking in Lebanon in the 1980s.
Hezbollah wasted little time in blaming Israel for his death in a car bomb in Damascus.
The group is thought to have been trying to avenge his death ever since.
'Revenge'
Investigative journalist Mr Bergman says the past three to four years have seen the Hamas, Hezbollah, Iran and Syria alliance "far more exposed" by Israeli intelligence, and on the defensive.
Even in recent weeks, the deaths of two Hamas members in a bombing in Lebanon, an attempt to bomb an Israeli diplomatic convoy in Jordan, and the mysterious killing of an Iranian scientist - though a quantum physicist, not a nuclear specialist - offer more material for speculation.
Targeting Mr Mabhouh would fit with Israel's historical policy, Mr Bergman adds.
"In some cases Israel has decided to close the circle and take revenge on people who were behind symbolic acts of terrorism - not necessary the most violent or lethal acts," he said.
And this can happen years after the incident in question.
Hamas claims Mr Mabhouh is the mastermind of the capture and killing of two Israeli soldiers, Avi Sasportas and Ilan Saadon, in 1989.
Sgt Sasportas's body was located seven years later, from a sketched map supplied by the Palestinians, and dug up from underneath a road that had been built over it.
The incident was an emotional one for the public in a country where most people serve in the military.
Mr Mabhouh's brother said Israel had been trying to kill him for years, and had unsuccessfully attempted to poison him six months earlier in Beirut.
But the reports remain confusing, with allegations that he was electrocuted, suffocated and poisoned all circulating - as well as reports that Hamas initially announced that he had died from bone disease a week earlier.
And this incident, like many before it, may remain shrouded in mystery, even as Hamas vows to take revenge.
