Whether the ICC has jurisdiction in Gaza is expected to be a highly contentious legal issue, and the ICC investigation comes at a time of heightened debate over the legality of Israel's Gaza campaign under international law.

This renewed debate has come about in large part due to statements made by Israeli Prime Minister Ehud Olmert on Sunday, in which he appeared to enshrine "disproportionate" response to provocations as official Israeli government policy.

On Tuesday, ICC chief prosecutor Luis Moreno-Ocampo made public a Jan. 21 letter from Palestinian Justice Minister Ali Khashan recognising the ICC's authority.

The ICC can only pursue investigations in states that have signed on to the Rome Statute creating the court, which Israel has not done. Khashan's letter was intended to give the ICC jurisdiction to launch an investigation in Gaza.

But the Palestinian move to recognise the court raises a set of murky legal issues, the foremost of which is whether the PNA can be considered a state. The PNA has argued that it can be considered the de facto sovereign authority in the Gaza Strip due to Israel's withdrawal from the territory in 2005.

If so, then Israel's non-recognition of the court would not prevent a war crimes investigation, since the only relevant factor is whether the alleged violations occurred in the territory of a signatory. If not, then the Gaza Strip would be considered Israeli territory and the ICC would have no jurisdiction to investigate.

Moreno-Ocampo indicated that one of the foci of his preliminary investigation would be to determine whether the ICC has the authority to proceed further. "The office of the prosecutor will carefully investigate all relevant issues, including on jurisdiction," he said in a statement.

Sean Murphy, a law professor at George Washington University, told IPS that the lack of international consensus about the PNA's status meant that the success or failure of the Palestinian move might depend on the authorities in The Hague.

"It's possible to file a declaration on an ad hoc basis, in accordance with the Rome Statute," Murphy said. "The question is whether the registrar would accept it, given that they would be having to make a decision on statehood in the face of widespread international disagreement".

Asked if he thought that the PNA's move would lead to any tangible results, Murphy said that he found it "unlikely - but stranger things have happened".

Human rights groups have called for an investigation into alleged Israeli war crimes during the three-week Gaza war, including the killing of civilians and the use of white phosphorus against human targets.

But debate over the war's legality has gone beyond the use of specific tactics by Israeli commanders on the ground, to question whether the campaign as a whole was in violation of international law.

This broader debate became far more contentious on Sunday, when Olmert responded to continued rocket attacks from Gaza into southern Israel by promising a "disproportionate" Israeli military response.

"The government's position was from the outset that if there is shooting at residents of the south there will be an Israeli response that will be harsh and disproportionate by its nature," Olmert said.

Although Olmert's remarks might be taken as mere blustering intended to deter further rocket attacks, his claim that the disproportionate use of force had been government policy "from the outset" was read by some as an acknowledgement that the Gaza campaign was disproportionate by design - and therefore in violation of international law.

Law professors interviewed by IPS were unsure as to whether Olmert's statement would have implications for any future criminal investigation. "Of course a statement like that could be used to show his knowledge and intent, but it would be small potatoes compared to the conduct of the conflict itself, the results of which are so clearly unlawful," University of Notre Dame law professor Mary Ellen O'Connell told IPS.

Still, it was clear that Olmert's remarks marked a major shift in the debates over the proportionality of Israeli military action.

The term "proportionality" has been used inconsistently and often inaccurately in these debates, but has generally referred to two criteria: whether the use of force is disproportionate to the threat that it responds to, and whether the civilian collateral damage in an attack is disproportionate to the military objective.

Israel has primarily been criticised according to the second criterion, which is enshrined in Article 51, Section 5 of the 1977 First Additional Protocol to the Geneva Conventions. It bans any "attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated".

Although Israel is not a signatory to the Additional Protocols, the Israeli Supreme Court has recognised the proportionality standard as binding, and during the Gaza campaign itself the Israeli government always maintained that it has met the standard.

A Dec. 29 statement by the Israeli Ministry of Foreign Affairs stated that "Israel has adopted the principles of international humanitarian law... and the Israel Defense Force (IDF) has enshrined them in its training, operational planning, and orders... [I]n relation to the question of proportionality, IDF doctrine requires a commander to refrain from an attack" that is expected to inflict excessive incidental harm.

Similarly, a few of Israel's defenders in the media have dismissed the proportionality standard entirely, but most - including prominent commentators such as Alan Dershowitz and Michael Walzer - have accepted the standard and argued that Israel's campaign adhered to it.

Following a war that claimed an estimated 1,300 Palestinian lives, hundreds of them civilians, the issue of proportionality became a pressing one for obvious reasons. But many scholars have argued that determining how much civilian harm is "excessive" with reference to a given military objective is so difficult that the proportionality standard is largely useless in practice and that violations of it are unlikely to result in any successful prosecution.

Still, although the proportionality debates have been largely unproductive to this point, Olmert's statement was noteworthy for its apparent abandonment of the proportionality standard altogether.

In doing so, he risks setting Israeli government policy on a course opposed to both international law and the rulings of the Israeli Supreme Court.

As the ICC mulls its potential investigation of the Gaza war, and the outcry against alleged human rights violations during the war increases, the debate about the campaign's overall legality is likely to become more contentious rather than less.