Founded as a Jewish homeland and post-Holocaust haven, forged in border wars with Arab forces, Israel now confronts a redefinition of the conflict after Palestinian refugees massed fearlessly on its frontiers. The thousands of protesters who surged from Syria, Lebanon and Gaza on Sunday, flattening some buffer-zone fences and drawing deadly Israeli gunfire, reminded many in the country of the image-corroding consequences of pitting the region's mightiest military against stone-throwing demonstrators.

That the unprecedented rallies fired up annual Palestinian events mourning Israel's creation, and were mobilised like the citizen revolts of the "Arab Spring" welcomed by the West, only deepened Israeli doubt about finding acceptable countermeasures.

Repeats of the "Nakba Day" marches looked likely given the Palestinians' campaign to corner Israel at the U.N. assembly in September by declaring independence should peace stay stalled. "The danger is that more mass processions like these will appear, not necessarily near the border, but also other places," Defence Minister Ehud Barak said in a television interview, apparently referring to Jewish settlements in the occupied West Bank, where Palestinians want statehood, or even Israel itself.

"We're only at the outset. We could see more complex things and complex challenges in this area. I recommend not to expect plans to be prepared systematically and be ready right on time."

Most Israeli analysts wrote off any option of adapting police anti-riot tactics for such large-scale clashes over tense armistice lines. Some recommended sowing new minefields instead.

A senior Barak aide, Amos Gilad, hinted that Israel would hone and perhaps harshen its response. He likened the rallies to lethal raids guerrilla raids that plagued Israelis in the past. "We already had very tough challenges that looked impossible," he told Army Radio. "There were terrorist attacks by sea, of a kind we have not heard about in decades because of our (operational) successes. For many long years, we had suicide attacks. Now the country is quiet and stable."

ARMY SAYS SHOWED RESTRAINT

With its preparedness and prestige in question, Israel's military -- which killed at least 13 protesters before repelling the rest -- has described its conduct as restrained. "Had we opened fire in a bloodbath with dozens of fatalities, we would now find ourselves in a very different reality," chief spokesman Brigadier-General Yoav Mordechai said.

As it happened, marches in the West Bank passed relatively quietly, a testament to ongoing Israeli security coordination with the forces of U.S.-backed Palestinian President Mahmoud Abbas. Demonstrations were similarly contained in Jordan and Egypt, the only Arab states to have made peace with Israel.

Israeli officials accused the governments of Lebanon and Syria of encouraging the protesters to reach the borders. Syrian President Bashar al-Assad, they said, may have seen a reprieve in shifting the violence toward Israel after cracking down for weeks on domestic unrest against his authoritarian rule.

But the tinderbox issue of Palestinian refugees remains at root. Hundreds of thousands were dispossessed by the 1948 Middle East war and, along with millions of their descendants, they demand the right to return to lands lost to the Israelis.

Israel rules that out as demographic suicide and two decades' worth of American-sponsored peace efforts have often foundered over murky proposals -- never taken up formally by the Palestinian leadership -- that refugees be resettled elsewhere.

So even if U.S. President Barack Obama, who hosts Netanyahu in Washington on Friday, finds the elusive formula for reviving negotiations, it is unlikely to placate Nakba-style protesters.

"(Israel) lacks means to prevent the breaching of its borders by tens and hundreds of thousands of Palestinians who will succeed in organising and fulfilling the dream of return with their own feet," wrote Alex Fishman, defence analyst for Israel's best-selling Yedioth Ahronoth newspaper.

"The more people talk about the possibility of a diplomatic arrangement or the establishment of a Palestinian state, the right of return will become the flag of the Palestinian struggle."