A year after Israel earned itself a public-relations disaster by killing nine civilians aboard the MV Mavi Marmara, another flotilla is fitting out in Turkey to sail to Gaza.

And three weeks after last month's Nakba ("catastrophe") marches, marking the 1948 creation of Israel, ended with Palestinian deaths at border points, more marches to Israel's frontiers have been planned for today. June 5 is set aside to mark the anniversary of the Naksa ("setback"), the 1967 war, in which Israel occupied the West Bank and Gaza.

Efforts such as these remind the world of the Palestinian plight in a way which undermines global perceptions of Israel's legitimacy. No wonder Israel and the US, plainly alarmed, have been trying to discourage these initiatives.

The US has reportedly pressured nearby states to stop the Naksa observances (demonstrations have already been called off in Lebanon). And Washington has reportedly offered Turkey a sweetener: if it prevents this year's flotilla from raising anchor, it will be invited to host eventual talks between Israel and the now more united Palestinians.

This is so notional as to be laughable: talks, if they happen, would be merely more talks; the issues remain intractable.

To be sure, both acts of defiance are almost purely symbolic. There is a mechanism for Israel to approve humanitarian aid shipments to Gaza, and the partial opening of the Rafah border crossing from Egypt could improve conditions in Gaza (though access was again restricted yesterday). Indeed Hamas found enough building materials to construct an imposing monument, just unveiled in Gaza City, to those who died aboard the Marmara.

But although they are mere symbols, acts of defiance have real power over world opinion. Every time Israel tries to enforce the isolation of Gaza, by land or sea, it only isolates itself more deeply in global public opinion.

Each such event is a step towards world acceptance of a declaration of Palestinian sovereignty - and towards the de-legitimisation of Israel. That Hamas and Fatah have joined hands in the push for a future state underscores this reality.

And so the US is doing what it can, through diplomacy, to abort the massing on Israel's borders. Meanwhile Israel's military has promised a more sophisticated, less lethal approach this time, at sea and at land borders points. That is the very least Israel must do.