The tinderbox that is the Middle East has a history of flaring up suddenly. But even by its standards the escalation of the crisis threatening the region this weekend has been spectacular. Since June 25, when Hamas captured an Israeli soldier, Gaza has come to resemble a war zone. Israel responded with bombing raids on Hamas targets, while Palestinian militants fired rockets into southern Israel. It was only last Wednesday, however, that the conflagration spread.

The attack on Israel by Hezbollah fighters based in southern Lebanon was, as Ehud Olmert, the Israeli prime minister, put it, “an act of war”. The rocket attack on the town of Shlomi and surrounding farms, followed by a raid into Israel and the capture of two more soldiers, not only opened up a second front by demonstrating Hezbollah solidarity with Hamas, it also guaranteed a robust response.

There are those who say that Israel is too easily provoked; that the deaths of dozens of civilians is too big a price to pay for the uncertain fate of three captured soldiers. They would argue that by responding with military might it is playing into the hands of its enemies. On this view, its enemies can never hope to defeat Israel militarily, but by provoking a sufficiently violent response they can whip up an Arab storm. Iran, whose eccentric president has called for the destruction of the state of Israel, arms Hezbollah. Syria, which has ambitions to dominate Lebanon, provides a haven for the military leadership of Hamas.

If Hezbollah’s aim was to test whether Mr Olmert has the military mettle of Ariel Sharon, his predecessor, it has had its answer in spades. The images of destruction this weekend in Lebanon — the destroyed roads, shattered bridges and peppered airport — have been condemned by some commentators and politicians as disproportionate. But they are a reminder of an enduring truth: Israel will not be pushed around. Put bluntly, Israelis will judge their government’s response by its ability to defend them.

So how to resolve a crisis that has already reverberated around the world by hitting share prices and pushing up the price of oil to a record $78 a barrel? The presidents and prime ministers of the G8 industrialised countries, who convened last night in St Petersburg for their summit, should be in a position to offer leadership. But the record of these summits in achieving anything constructive is poor and the G8 is split in its attitudes to Israel.

Israel’s aims are simple: to get its soldiers back and to stop attacks on its own territory from within Gaza and Lebanon. Will its show of force achieve that end? In Lebanon, where the economic cost of Israel’s response can be seen in the exodus of the country’s tourists, the question is the leverage that the Lebanese government has over Hezbollah. In Gaza, it is whether Israel can bomb Hamas into submission. Some elements in Hamas may have been inching towards acceptance of the state of Israel before the fighting started. The Israeli right wing, meanwhile, will see events as proof that withdrawal from Gaza was an error and that each time its government makes concessions, its enemies take advantage.

This is a dangerous situation. Israeli missiles yesterday came close to straying into Syrian territory. History offers some reassurance that this will not spread into a region-wide conflict, although that can never be guaranteed. The road map to Middle East peace, which in 2003 envisaged “a final and comprehensive settlement of the Israeli-Palestinian conflict by 2005”, has not yet been torn up. But it is, as Kofi Annan, the United Nations secretary-general, pointed out, becalmed by the refusal of the Palestinian Authority to condemn terrorist attacks on Israel since Hamas’s election victory in 2006. The road map urgently needs to be revived. But this weekend the chances of a lasting settlement look as far off as ever.