Paul Reynolds BBC News Online World Affairs correspondent

By seeking the expulsion from the West Bank to Gaza of relatives suspected of helping Palestinian bombers and gunmen, Israel has opened a new front in its war of attrition.

In the instance of its kind, Israel has ordered the removal of three relatives - the brother and sister of a man said to been behind a bombing in Tel Aviv.

We have been forced to take unusual measures we had preferred to avoid

Mark Sofer, Israeli foreign ministry

The Israelis say that expulsions (and the demolition of the family homes of the bombers) are justified in reducing terrorism.

Mark Sofer, a foreign ministry spokesman, said: "The huge suicide attacks we have faced have forced us to take unusual measures that we had preferred to avoid."

But for the Palestinians, the move is another element of repression.

Ahmed Abdel-Rahman, one of Yasser Arafat's aides, said: "This is a declaration of the bankruptcy of Israel's military solution and reoccupation."

Deterring 'martyrs'

The Israeli aim is to punish and deter. In many cases, close relatives help a suicide or other attack by action or inaction.

The tactic is also designed to put an end to the Palestinian practice of families benefiting from and glorifying the death of a young man or woman who has blown him or herself up together with Israeli civilians.

Individual or mass forcible transfers ...are prohibited

Fourth Geneva Convention

One of the motives of the young men who volunteer for suicide attacks - martyrdom as they themselves call it - is that their families will be well looked after and, indeed, will be viewed heroically in their towns and villages.

If their families suffer, the Israeli reckoning is, there will be fewer volunteers.

'Breaching law'

The legality of the Israeli action in international law is strongly contested.

Israel acts on the basis of an old British law, the Defence (Emergency) Regulations, 1945, introduced when Britain was in charge of Palestine.

The intifada has been going on for nearly two years

This law allowed for deportations "for reasons of security" but limited the powers to "the most extreme cases."

Israel inherited the law from Jordan, it says, when it took over the West Bank and Gaza in 1967.

The Palestinians argue that it contravenes the Fourth Geneva Convention of 1949 which seeks to protect civilians.

While Israel does not accept the status of the West Bank and Gaza as "occupied", its soldiers are under orders to respect the Geneva Conventions

Article 49 states: "Individual or mass forcible transfers, as well as deportations of protected persons from occupied territory to the territory of the Occupying Power or to that of any other country, occupied or not, are prohibited, regardless of their motive."

But Israel counters that Article 49 was designed to stop Nazi or Balkan style ethnic cleansing and that it allows for exceptions.

The article also states: " The Occupying Power may undertake total or partial evacuation of a given area if the security of the population or imperative military reasons so demand."

While Israel does not accept the status of the West Bank and Gaza as "occupied", its soldiers are under orders to respect the Geneva Conventions.

Legal conditions

Israel's Supreme Court has in the past authorised demolitions and expulsions, but it has set conditions, the main one of which is that the military must argue for the absolute necessity of any action.

In 1992 the court allowed the expulsion to Lebanon of some Hamas and Islamic Jihad activists, but said that others should be allowed back at once and all should come back early.

Hamas has vowed to continue its campaign

In the event, they came back eventually anyway when the Israeli Government backed down in the face of international criticism.

In the present case, the Attorney General Elyakim Rubenstein restricted the number of relatives whose expulsion was sought, because in his view expulsions should be confined only to those who directly help the bombers.

Casting the net too widely would - in his view and probably that of the court - run foul of Article 33 of the Fourth Convention which says that "collective penalties... are prohibited".

The article states: "No protected person may be punished for an offence he or she has not personally committed."

These legal definitions do not impress Palestinians whose leader Yasser Arafat has described the Israeli actions as "a crime against international and humanitarian law".