The Quartet of Middle East peace negotiators on Monday welcomed Israel's decision to ease its blockade of Gaza but said the situation in the territory remained "unsustainable and unacceptable".

In a statement agreed during a conference call, the Quartet -- the United States, European Union, Russia and the United Nations -- said Israel's change of policy towards Gaza was encouraging but said much more needed to be done to alleviate pressure on the Palestinian territory's population.

"The new policy towards Gaza just announced by the government of Israel is a welcome development," read a statement agreed after the call, which involved Quartet envoy Tony Blair, U.S. special envoy George Mitchell and EU foreign affairs representative Catherine Ashton, among others.

"Full and effective implementation will comprise a significant shift in strategy towards meeting the needs of Gaza's population for humanitarian and commercial goods, civilian reconstruction and infrastructure, and legitimate economic activity, as well as the security needs of Israel."

But the statement added that the "current situation in Gaza, including the humanitarian and human rights situation of the civilian population, is unsustainable, unacceptable, and not in the interests of any of those concerned."

Israel said on Sunday it would move to allow almost all goods into Gaza except for arms and materials used to make them, a shift from its previous policy of banning virtually all goods from entering the coastal territory of 1.5 million people.

The decision followed intense international pressure and criticism of Israel after its deadly raid on a flotilla of aid ships which tried to break the Gaza blockade on May 31.

Fighting erupted as Israeli commandos boarded one of the ships, and nine Turkish men were shot dead by Israeli forces. Relations between Israel and Turkey, once solid allies, have since sunk to their lowest level in decades.

The Quartet said it would continue to press Israel, the Palestinian Authority and other parties -- a reference to Egypt, which also borders Gaza -- to ensure the new arrangements for Gaza's crossings were implemented as quickly as possible.

"The Quartet affirms that much work remains to achieve fully the situation stated above ... It will monitor closely the implementation of the policy in all its aspects," it said.

At the same time, the Quartet reiterated the need for Israel's "legitimate security concerns" to be safeguarded and said it would work with the international community to prevent the traffickng of arms and ammunition into Gaza.

It also called for the immediate release of Gilad Shalit, an Israel soldier captured by Gaza militants on June 25, 2006, and condemned Hamas, the militant group that has run Gaza since June 2007, for not allowing the Red Cross access to Shalit.