Israel has been killing those it considers a threat to its security for decades but, in the past few years, the policy has been stepped up as part of the government's attempts to stop suicide attacks.
Israel has vowed to target militants wherever they are
Since the start of the Palestinian intifada in September 2000, dozens of Hamas and Islamic Jihad militants have been killed.
These "targeted killings," as they are known in Israel, were described by Israeli officials three years ago as "rare and exceptional" measures. But they have increased in regularity.
Targets have included what the Israeli army refers to as the "ticking time bombs", the suicide bombers, as well as militant leaders such as Hamas founder Sheikh Yassin and less than a month later the group's Gaza chief, Abdel Aziz al-Rantissi.
The operations have involved either large Israeli military forces, small teams or individuals from the security forces or missile attacks from combat aircraft and helicopters.
HIGH PROFILE TARGETS
April 2004: Abdel Aziz al-Rantissi, Hamas leader in Gaza, killed
March 2004: Sheikh Ahmed Yassin, Hamas founder, killed
September 2003: Sheikh Yassin survives assassination attempt
August 2003: Ismail Abu Shanab, leading Hamas figure, killed
June 2003: Rantissi survives assassination attempt
July 2002: Salah Shahada, head of Hamas' military wing in Gaza, killed
September 1997: Mossad botches attempt to kill Hamas political leader Khaled Mashaal, in Jordan
January 1996: Yahya Ayyash, Hamas militant known as The Engineer killed for his role in a bomb attacks
The use of air strikes has frequently resulted in the deaths of innocent bystanders.
According to a recent report by one Palestinian human rights group, more than 150 Palestinians had been targeted and killed by Israelis and more than 60 bystanders had been killed.
Israel's policy became one of the most divisive issues in the debate over a US-backed peace plan known as the road map.
Palestinian militant leaders said they would only honour a ceasefire agreement if Israel ended the killings.
But Israeli officials said they reserved the right to target militants that they considered threats if the Palestinian security forces did not detain them or help prevent suicide attacks.
The policy has provoked international criticism, particularly from the European Union, the UK and Arab nations. The US has criticised the policy as "unhelpful" to the peace effort but has not issued strong condemnations.
Human rights groups within Israel and abroad have often condemned the strikes, pointing out the high rate of civilian casualties and the legal question of carrying out what amounts to execution without trial.
Israel, which has lost hundreds of civilians to suicide attacks, says the tactic is a legitimate because those killed by its security forces are directly involved in the planning and execution of attacks against Israeli citizens.
It also maintains that the only way to fight the militant groups is to remove some of its leaders.
Yassin escaped an assassination attempt before he was killed
Sheikh Yassin and Rantissi are the most significant militant figures to have been killed by Israel since the outbreak of the intifada.
Both escaped earlier attempts on their lives by the Israeli armed forces, but both became victims of missile strikes.
The assassinations provoked condemnation from Arab and European countries while each time the US called for all sides to remain calm.
Hamas warned that the September 2003 attempt on Sheikh Yassin would open "the gates of hell". though Israeli Prime Minister Ariel Sharon remained defiant, saying that Hamas leaders were all "marked for death".
There is another objection to the tactic: That it does not work in its own goal of preventing violence.
Attacks against leaders of the Hamas and Islamic Jihad militant groups nearly always spark or fuel a cycle of violence.
In one example of this late last year, Israel on Christmas Day, targeted and killed two senior Islamic Jihad men. Three civilians also lost their lives.
Hours later, a Palestinian bomber killed himself and three Israeli civilians in Tel Aviv.
In response, Israeli troops mounted an incursion in to the West Bank city of Nablus. This was followed shortly afterwards by a Palestinian suicide bombing close to the border of Israel and the Gaza Strip.
Hamas vowed revenge for Sheikh Yassin and made similar threats in the wake of Rantissi's killing, prompting fears of more deadly retaliation.