'We knew there was a chance this would happen," said Ashkelon's Mayor Roni Mehatzri, of the Kassam rocket that plunged into the playground of a school in the heart of his city on Tuesday. "But it still surprised us." Israel had indeed been braced for many months for what was deemed the inevitable extension of the Kassams' range to Ashkelon. Mercifully, Tuesday's attack caused no casualties. But Israel is braced for that eventuality, too, and for the possibility of a rocket hitting one of the southern city's more sensitive infrastructure installations and causing far wider damage. As the Kassams rained down on Sderot in recent weeks, that city's mayor, Eli Moyal, observed at one point that the terror groups were firing the "same drek" that they had been launching for years. Plainly now, however, the rockets are being refined and improved. Plainly, too, the notion that the Kassam threat could be met via the defensive reinforcing of homes in a limited target zone has been superseded. The fact that a Kassam hit Ashkelon even as the IDF military focus on Gaza is higher than at any time since Israel pulled out of the Strip last summer also underlines the appalling ease with which these rockets can be launched. As Eliezer Shkedy, the commander of the Israel Air Force, told The Jerusalem Post in an interview last week, "Setting up to fire from a backyard has not been a problem for [the Kassam crews] and won't be a problem for them." Even when Israel had troops on the ground in Gaza, he noted, "they kept firing." Thus as Israel apparently gears up for the creation of some kind of "buffer zone" in northern Gaza, the limitations of such a presence are already clear: An ever-extended range for the Kassams would require an ever-deeper buffer zone, and even such a zone cannot fully thwart the fire when the rocket launchers can be so rapidly set up and dismantled. The full answer to the Kassams lies in something else Shkedy told the Post. The rocket attacks will only completely stop, he said, when "they'll decide it's not in their interest to fire." That, now, is the challenge for Israel: to create the circumstances in which the Kassam crews, and those who could choose to rein them in, decide that their vital interest lies in putting aside the rockets. And that can only be done by raising the price these attacks impose on the Palestinian leadership. Israel's withdrawal from Gaza was, in part, an attempt to force the Palestinian leadership to take responsibility for the territory. It was a test that the Palestinians have so far failed. That failure, and its repercussions, are central to the falling Israeli support for further unilateral withdrawals in the West Bank. However the immediate issue is not Olmert's "realignment" options, but, rather, deterring further attacks from Gaza. In part mindful of the implications for captured soldier Gilad Shalit, Israel has not used the full range of its military options in Gaza. It opted yesterday to target institutions and infrastructure that "serve terrorism" there and in the West Bank, and to take further steps to restrict terrorists' freedom of movement in Strip. But it has also given indications of what it might deem necessary, notably with the unexpected arrests last week of dozens of Hamas ministers and legislators. Crucially, it has made plain that it will hold the political representatives of Hamas directly responsible for the terrorist mindset they foster and for the terrorist actions they endorse and hail. To date, as the Ashkelon attack illustrates, the implications of that concept of direct responsibility have not been fully internalized by Hamas's leaders. They would do well to rethink. International diplomatic action has to be part of the deterrent capability, too. While international calls for the release of Shalit are welcome and good, the US-UN-EU-Russia Quartet needs to do more to demonstrate that missile attacks against Israel are unacceptable. It needs to make clear that it appreciates which party is the aggressor in this escalating conflict, and that Israel will receive full support when taking responses designed to put an end to the attacks.