(Reuters) -

The possibility of a war crimes investigation into the conduct of Israeli forces in Gaza, until recently unthinkable, has grown after the Palestinians said this week they wanted to become a party to the International Criminal Court.

The world's permanent war crimes court in The Hague declined two years ago to investigate allegations against the Israeli military in 2008-2009, citing the uncertain legal status of the Palestinian Authority.

A lot has changed since then.

Fresh allegations of war crimes have flowed in recent weeks from fighting in Gaza, where Israel responded to a surge in rocket attacks by Hamas militants with air strikes and a ground incursion. The Palestinians this week unexpectedly said they are just one procedural step away from ICC membership.

The legal groundwork for such a move was laid in Nov 2012 when the 193-member U.N. General Assembly overwhelmingly approved the de facto recognition of the sovereign state of Palestine by upgrading the Palestinian Authority's observer status to "non-member state" from "entity.”

If the Palestinians were to sign the ICC's founding treaty, the Rome Statute, the court would have jurisdiction over crimes committed in the Palestinian territories.

With Palestinian authorization, an ICC investigation could then examine events as far back as July 1, 2002, when the court opened with a mandate to try individuals for war crimes, crimes against humanity and genocide.

"If Palestine applies it will be admitted to the ICC," John Dugard, international law professor and a former U.N. Special Rapporteur for the Palestinian territories, told Reuters.

"The U.N. has spoken and it has recognized the state of Palestine and it is now for the ICC to admit Palestine. I cannot see how that can be resisted."

Dugard said the Palestinians could then ask prosecutors to investigate alleged crimes in July and August in Gaza, but also the legality of Israeli West Bank settlements.